## 2017 |
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100. | Picchi, Davide; Poesio, Pietro; Ullmann, Amos; Brauner, Neima Characteristics of stratified flows of Newtonian/non-Newtonian shear-thinning fluids Journal Article International Journal of Multiphase Flow (accepted), 2017. Abstract | BibTeX | Tags: Hold-up, Multiple Hold-up solutions, shape factor, Shear-thinning fluid, Stratified flow, Two-fluid model | Links: @article{Picchi_Poesio_Ullmann_Brauner_2017, title = {Characteristics of stratified flows of Newtonian/non-Newtonian shear-thinning fluids}, author = {Davide Picchi and Pietro Poesio and Amos Ullmann and Neima Brauner}, doi = {10.1016/j.ijmultiphaseflow.2017.06.005}, year = {2017}, date = {2017-06-13}, journal = {International Journal of Multiphase Flow (accepted)}, abstract = {Exact solutions for laminar stratified flows of Newtonian/non-Newtonian shear-thinning fluids in horizontal and inclined channels are presented. An iterative algorithm is proposed to compute the laminar solution for the general case of a Carreau non-Newtonian fluid. The exact solution is used to study the effect of the rheology of the shear-thinning liquid on two-phase flow characteristics considering both gas/liquid and liquid/liquid systems. Concurrent and counter-current inclined systems are investigated, including the mapping of multiple solution boundaries. Aspects relevant to practical applications are discussed, such as the insitu hold-up, or lubrication effects achieved by adding a less viscous phase. A characteristic of this family of systems is that, even if the liquid has a complex rheology (Carreau fluid), the two-phase stratified flow can behave like the liquid is Newtonian for a wide range of operational conditions. The capability of the two-fluid model to yield satisfactory predictions in the presence of shear-thinning liquids is tested, and an algorithm is proposed to a priori predict if the Newtonian (zero shear rate viscosity) behaviour arises for a given operational conditions in order to avoid large errors in the predictions of flow characteristics when the power-law is considered for modelling the shear-thinning behaviour. Two-fluid model closures implied by the exact solution and the effect of a turbulent gas layer are also addressed.}, keywords = {Hold-up, Multiple Hold-up solutions, shape factor, Shear-thinning fluid, Stratified flow, Two-fluid model}, pubstate = {published}, tppubtype = {article} } Exact solutions for laminar stratified flows of Newtonian/non-Newtonian shear-thinning fluids in horizontal and inclined channels are presented. An iterative algorithm is proposed to compute the laminar solution for the general case of a Carreau non-Newtonian fluid. The exact solution is used to study the effect of the rheology of the shear-thinning liquid on two-phase flow characteristics considering both gas/liquid and liquid/liquid systems. Concurrent and counter-current inclined systems are investigated, including the mapping of multiple solution boundaries. Aspects relevant to practical applications are discussed, such as the insitu hold-up, or lubrication effects achieved by adding a less viscous phase. A characteristic of this family of systems is that, even if the liquid has a complex rheology (Carreau fluid), the two-phase stratified flow can behave like the liquid is Newtonian for a wide range of operational conditions. The capability of the two-fluid model to yield satisfactory predictions in the presence of shear-thinning liquids is tested, and an algorithm is proposed to a priori predict if the Newtonian (zero shear rate viscosity) behaviour arises for a given operational conditions in order to avoid large errors in the predictions of flow characteristics when the power-law is considered for modelling the shear-thinning behaviour. Two-fluid model closures implied by the exact solution and the effect of a turbulent gas layer are also addressed. | |

99. | Ferrari, Marco; Bonzanini, Arianna; Poesio, Pietro A five-equation, transient, hyperbolic, one-dimensional model for slug capturing in pipes Journal Article International Journal for Numerical Methods in Fluids, 2017. Abstract | BibTeX | Tags: Finite volume, Hyperbolic, Partial differential equations, slug capturing, Two-fluid model, Two-phase flow | Links: @article{Ferrari_Bonzanini_2017, title = {A five-equation, transient, hyperbolic, one-dimensional model for slug capturing in pipes}, author = {Marco Ferrari and Arianna Bonzanini and Pietro Poesio}, doi = {10.1002/fld.4387}, year = {2017}, date = {2017-06-01}, journal = {International Journal for Numerical Methods in Fluids}, abstract = {A novel numerical scheme for slug capturing in pipes using a 1D transient hyperbolic five-equation two-fluid model is presented. Previous work has shown that one-dimensional two-fluid models are able to capture slug flow automatically. In this work a similar approach is further developed using a new numerical scheme, applied to a hyperbolic five-equation two-fluid model. Starting from a finite volume discretisation of a five equations two-fluid hyperbolic model and adding appropriate closure relations, a second-order code is implemented and applied to air-water flows in horizontal pipes, simulating the two-phase to one-phase flow process. The code is evaluated in some common standard test cases. A slug capturing application is also discussed.We show, in an air/water horizontal pipe, slug initiation, growth and development. Moreover, a grid refinement analysis is performed showing that the method is grid independent and we show the code capability to take into account eventual surface tension effects, through the instantaneous pressure relaxation process. Finally, a prediction of flow regime transitions is shown and compared to a well-known theoretical flow pattern map in addition to a preliminary comparison of computed slug characteristics against well-known empirical correlations.}, keywords = {Finite volume, Hyperbolic, Partial differential equations, slug capturing, Two-fluid model, Two-phase flow}, pubstate = {published}, tppubtype = {article} } A novel numerical scheme for slug capturing in pipes using a 1D transient hyperbolic five-equation two-fluid model is presented. Previous work has shown that one-dimensional two-fluid models are able to capture slug flow automatically. In this work a similar approach is further developed using a new numerical scheme, applied to a hyperbolic five-equation two-fluid model. Starting from a finite volume discretisation of a five equations two-fluid hyperbolic model and adding appropriate closure relations, a second-order code is implemented and applied to air-water flows in horizontal pipes, simulating the two-phase to one-phase flow process. The code is evaluated in some common standard test cases. A slug capturing application is also discussed.We show, in an air/water horizontal pipe, slug initiation, growth and development. Moreover, a grid refinement analysis is performed showing that the method is grid independent and we show the code capability to take into account eventual surface tension effects, through the instantaneous pressure relaxation process. Finally, a prediction of flow regime transitions is shown and compared to a well-known theoretical flow pattern map in addition to a preliminary comparison of computed slug characteristics against well-known empirical correlations. | |

98. | Poesio, Pietro; Damone, Angelo; Matar, Omar Slip at liquid-liquid interfaces Journal Article Physical Review Fluids, 2 (4), pp. 044004, 2017. Abstract | BibTeX | Tags: Coarse graining, Density functional theory, liquid-liquid interfaces, Molecular Dynamics, multiphase flow, Nanoscale flows | Links: @article{Poesio_Damone_Matar_2017, title = {Slip at liquid-liquid interfaces}, author = {Pietro Poesio and Angelo Damone and Omar K. Matar}, doi = {10.1103/PhysRevFluids.2.044004}, year = {2017}, date = {2017-04-27}, journal = {Physical Review Fluids}, volume = {2}, number = {4}, pages = {044004}, abstract = {In this manuscript, we address a problem of fundamental importance in the physics of interfaces, which is central to the description of multiphase fluid dynamics. This work is important to study interfaces in systems such as polymer melts and solutions, where velocity jumps have been observed and interpreted as a manifestation of slip. This is in violation of classical interfacial conditions that require continuity of velocity, and has been remedied in the literature via use of ad hoc models, such as the so-called Navier slip condition. The paper suggests that it is possible to obviate completely the need for such an approach. Instead, we show that one simply requires knowledge of the density field and the molar fraction of the fluid components, and the dependence of the viscosity on the density. This information can be obtained easily through a molecular dynamics simulations.}, keywords = {Coarse graining, Density functional theory, liquid-liquid interfaces, Molecular Dynamics, multiphase flow, Nanoscale flows}, pubstate = {published}, tppubtype = {article} } In this manuscript, we address a problem of fundamental importance in the physics of interfaces, which is central to the description of multiphase fluid dynamics. This work is important to study interfaces in systems such as polymer melts and solutions, where velocity jumps have been observed and interpreted as a manifestation of slip. This is in violation of classical interfacial conditions that require continuity of velocity, and has been remedied in the literature via use of ad hoc models, such as the so-called Navier slip condition. The paper suggests that it is possible to obviate completely the need for such an approach. Instead, we show that one simply requires knowledge of the density field and the molar fraction of the fluid components, and the dependence of the viscosity on the density. This information can be obtained easily through a molecular dynamics simulations. | |

97. | Picchi, Davide; Poesio, Pietro Uncertainty quantification and global sensitivity analysis of mechanistic one-dimensional models and flow pattern transition boundaries predictions for two-phase pipe flows Journal Article International Journal of Multiphase Flow, 90 , pp. 64-78, 2017. Abstract | BibTeX | Tags: Confidence level, flow pattern transition, Pressure drops, Sobol’s indices, Two-fluid model, uncertainty quantification | Links: @article{Picchi_2016, title = {Uncertainty quantification and global sensitivity analysis of mechanistic one-dimensional models and flow pattern transition boundaries predictions for two-phase pipe flows}, author = {Davide Picchi and Pietro Poesio}, doi = {10.1016/j.ijmultiphaseflow.2016.12.004}, year = {2017}, date = {2017-04-01}, journal = {International Journal of Multiphase Flow}, volume = {90}, pages = {64-78}, abstract = {The prediction of uncertainties is a growing interest in flow assurance industrial applications, but only few works have been presented on this topic. In this work, an uncertainty quantification and a global sensitivity analysis are performed to quantify the level of confidence in predictions of one- dimensional mechanistic models considering different two-phase flow regimes. A method is proposed for this purpose accounting for the effect of several variables on pressure drop and hold-up predictions by the well known one-dimensional two-fluid model, such as fluid flow rates, geometry (the inclination angle and the pipe diameter), and fluid properties (density and viscosity); the case of a non-Newtonian power-law fluid behaviour is also considered. Flow pattern transition boundaries, including the stability of the stratified flow regime, are included in this analysis. Monte Carlo simulations were used for the uncertainty quantifications and different models for the sensitivity analysis, such as scatter plot, linear regression, the Morris’s method, and the Sobol’s Method, were used and compared to identify the best tool for this family of models. The Sobol’s method appears to be the most convenient approach and a discussion is provided considering different practical cases for gas/liquid and liquid/liquid systems. The most critical input parameters in terms of uncertainty are rigorously identified case by case. A way to reduce the output uncertainty is indicated by the interpretation of the results of the global sensitivity analysis. The conclusions of this analysis gives new insights regarding the degree of uncertainties in predictions of one- dimensional mechanistic models. }, keywords = {Confidence level, flow pattern transition, Pressure drops, Sobol’s indices, Two-fluid model, uncertainty quantification}, pubstate = {published}, tppubtype = {article} } The prediction of uncertainties is a growing interest in flow assurance industrial applications, but only few works have been presented on this topic. In this work, an uncertainty quantification and a global sensitivity analysis are performed to quantify the level of confidence in predictions of one- dimensional mechanistic models considering different two-phase flow regimes. A method is proposed for this purpose accounting for the effect of several variables on pressure drop and hold-up predictions by the well known one-dimensional two-fluid model, such as fluid flow rates, geometry (the inclination angle and the pipe diameter), and fluid properties (density and viscosity); the case of a non-Newtonian power-law fluid behaviour is also considered. Flow pattern transition boundaries, including the stability of the stratified flow regime, are included in this analysis. Monte Carlo simulations were used for the uncertainty quantifications and different models for the sensitivity analysis, such as scatter plot, linear regression, the Morris’s method, and the Sobol’s Method, were used and compared to identify the best tool for this family of models. The Sobol’s method appears to be the most convenient approach and a discussion is provided considering different practical cases for gas/liquid and liquid/liquid systems. The most critical input parameters in terms of uncertainty are rigorously identified case by case. A way to reduce the output uncertainty is indicated by the interpretation of the results of the global sensitivity analysis. The conclusions of this analysis gives new insights regarding the degree of uncertainties in predictions of one- dimensional mechanistic models. | |

96. | Beretta, Gian Paolo; Al-Abbasi, Omar; von Spakovsky, Michael Steepest-entropy-ascent nonequilibrium quantum thermodynamic framework to model chemical reaction rates at an atomistic level Journal Article Physical Review E, 95 , pp. 042139, 2017. Abstract | BibTeX | Tags: atomistic chemical theory, quantum thermodinamics, steepest-entropy-ascent @article{Beretta_2017, title = {Steepest-entropy-ascent nonequilibrium quantum thermodynamic framework to model chemical reaction rates at an atomistic level}, author = {Gian Paolo Beretta and Omar Al-Abbasi and Michael R. von Spakovsky}, year = {2017}, date = {2017-03-25}, journal = {Physical Review E}, volume = {95}, pages = {042139}, abstract = {The steepest entropy ascent (SEA) dynamical principle provides a general framework for modeling the dynamics of nonequilibrium (NE) phenomena at any level of description, including the atomistic one. It has recently been shown to provide a precise implementation and meaning to the maximum entropy production principle and to encompass many well-established theories of nonequilibrium thermodynamics into a single unifying geometrical framework. Its original formulation in the framework of quantum thermodynamics (QT) assumes the simplest and most natural Fisher-Rao metric to geometrize from a dynamical standpoint the manifold of density operators, which represent the thermodynamic NE states of the system. This simplest SEAQT formulation is used here to develop a general mathematical framework for modeling the NE time evolution of the quantum state of a chemically reactive mixture at an atomistic level. The method is illustrated for a simple two-reaction kinetic scheme of the overall reaction F + H2 iff HF + F in an isolated tank of fixed volume. However, the general formalism is developed for a reactive system subject to multiple reaction mechanisms. To explicitly implement the SEAQT nonlinear law of evolution for the density operator, both the energy and the particle number eigenvalue problems are set up and solved analytically under the dilute gas approximation. The system-level energy and particle number eigenvalues and eigenstates are used in the SEAQT equation of motion to determine the time evolution of the density operator, thus, effectively describing the overall kinetics of the reacting system as it relaxes towards stable chemical equilibrium. The predicted time evolution in the near-equilibrium limit is compared to the reaction rates given by a standard detailed kinetic model so as to extract the single time constant needed by the present SEA model.}, keywords = {atomistic chemical theory, quantum thermodinamics, steepest-entropy-ascent}, pubstate = {published}, tppubtype = {article} } The steepest entropy ascent (SEA) dynamical principle provides a general framework for modeling the dynamics of nonequilibrium (NE) phenomena at any level of description, including the atomistic one. It has recently been shown to provide a precise implementation and meaning to the maximum entropy production principle and to encompass many well-established theories of nonequilibrium thermodynamics into a single unifying geometrical framework. Its original formulation in the framework of quantum thermodynamics (QT) assumes the simplest and most natural Fisher-Rao metric to geometrize from a dynamical standpoint the manifold of density operators, which represent the thermodynamic NE states of the system. This simplest SEAQT formulation is used here to develop a general mathematical framework for modeling the NE time evolution of the quantum state of a chemically reactive mixture at an atomistic level. The method is illustrated for a simple two-reaction kinetic scheme of the overall reaction F + H2 iff HF + F in an isolated tank of fixed volume. However, the general formalism is developed for a reactive system subject to multiple reaction mechanisms. To explicitly implement the SEAQT nonlinear law of evolution for the density operator, both the energy and the particle number eigenvalue problems are set up and solved analytically under the dilute gas approximation. The system-level energy and particle number eigenvalues and eigenstates are used in the SEAQT equation of motion to determine the time evolution of the density operator, thus, effectively describing the overall kinetics of the reacting system as it relaxes towards stable chemical equilibrium. The predicted time evolution in the near-equilibrium limit is compared to the reaction rates given by a standard detailed kinetic model so as to extract the single time constant needed by the present SEA model. | |

## 2016 |
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95. | Picchi, Davide; Poesio, Pietro Stability of multiple solutions in inclined gas/shear-thinning fluid stratified pipe flow Journal Article International Journal of Multiphase Flow, 84 , pp. 176-187, 2016. Abstract | BibTeX | Tags: counter-current flows, dissipation, multiple solutions, Shear-thinning fluid, Stratified flow, structural stability | Links: @article{Picchi_Poesio_2016, title = {Stability of multiple solutions in inclined gas/shear-thinning fluid stratified pipe flow}, author = {Davide Picchi and Pietro Poesio}, doi = {10.1016/j.ijmultiphaseflow.2016.03.002}, year = {2016}, date = {2016-09-01}, journal = {International Journal of Multiphase Flow}, volume = {84}, pages = {176-187}, abstract = {This work provides an investigation on multiple solutions for gas/shear-thinning fluid inclined stratified pipe flows. Multiple solution operative conditions are studied investigating the effect of the interfacial shear stress modeling and the rheology of the shear-thinning fluid. The modeling of the interfacial shear stress has a strong influence on multiple solutions regions for counter-current flows. The stability of multiple hold-up solutions is studied considering the structural stability, the interfacial stability, and the minimization of the dissipation ap- proaches. The results of the three different approaches are commented both for concurrent and counter-current flows, giving the same conclusions only for upward inclined flows.}, keywords = {counter-current flows, dissipation, multiple solutions, Shear-thinning fluid, Stratified flow, structural stability}, pubstate = {published}, tppubtype = {article} } This work provides an investigation on multiple solutions for gas/shear-thinning fluid inclined stratified pipe flows. Multiple solution operative conditions are studied investigating the effect of the interfacial shear stress modeling and the rheology of the shear-thinning fluid. The modeling of the interfacial shear stress has a strong influence on multiple solutions regions for counter-current flows. The stability of multiple hold-up solutions is studied considering the structural stability, the interfacial stability, and the minimization of the dissipation ap- proaches. The results of the three different approaches are commented both for concurrent and counter-current flows, giving the same conclusions only for upward inclined flows. | |

94. | Picchi, Davide; Poesio, Pietro A unified model to predict flow pattern transitions in horizontal and slightly inclined two-phase gas/shear-thinning fluid pipe flows Journal Article International Journal of Multiphase Flow, 84 , pp. 279-291, 2016. Abstract | BibTeX | Tags: annular flow, dispersed flow, flow pattern transition, non-linear stability, Shear-thinning fluid, Stratified flow | Links: @article{Picchi_Poesio_2016_2, title = {A unified model to predict flow pattern transitions in horizontal and slightly inclined two-phase gas/shear-thinning fluid pipe flows }, author = {Davide Picchi and Pietro Poesio}, doi = {10.1016/j.ijmultiphaseflow.2016.04.010}, year = {2016}, date = {2016-09-01}, journal = {International Journal of Multiphase Flow}, volume = {84}, pages = {279-291}, abstract = {Flow pattern transitions in two-phase gas/shear-thinning fluid pipe flows represent a key aspect during oil transportation and in chemical industry. In this paper a unified model to build a complete flow pattern map is proposed and models to predict flow patterns are provided. The transitions from stratified flow regime are investigates performing a linear stability and well-posedness analyses, and a non-linear stability analysis. The steady and fully developed two-fluid model for the annular flow is proposed and validated; the flow pattern transition from the annular flow is discussed considering, also, the structural stability. The transition to dispersed flow, the slug stability approach, and criteria to obtain the slug/plug and the bubbly/plug boundaries are considered. A sensitivity analysis on the effect of the rheology of the shear- thinning fluid on flow pattern boundaries is carried out and, then, the complete flow pattern maps are validated with data taken from the literature showing a good agreement. }, keywords = {annular flow, dispersed flow, flow pattern transition, non-linear stability, Shear-thinning fluid, Stratified flow}, pubstate = {published}, tppubtype = {article} } Flow pattern transitions in two-phase gas/shear-thinning fluid pipe flows represent a key aspect during oil transportation and in chemical industry. In this paper a unified model to build a complete flow pattern map is proposed and models to predict flow patterns are provided. The transitions from stratified flow regime are investigates performing a linear stability and well-posedness analyses, and a non-linear stability analysis. The steady and fully developed two-fluid model for the annular flow is proposed and validated; the flow pattern transition from the annular flow is discussed considering, also, the structural stability. The transition to dispersed flow, the slug stability approach, and criteria to obtain the slug/plug and the bubbly/plug boundaries are considered. A sensitivity analysis on the effect of the rheology of the shear- thinning fluid on flow pattern boundaries is carried out and, then, the complete flow pattern maps are validated with data taken from the literature showing a good agreement. | |

93. | Losi, Gianluca; Arnone, Davide; Correra, Sebastiano; Poesio, Pietro Modelling and statistical analysis of high viscosity oil/air slug flow characteristics in a small diameter horizontal pipe Journal Article Chemical Engineering Science, 148 , pp. 190-202, 2016. Abstract | BibTeX | Tags: Pressure drops, Slug flow, slug flow model, slug lengths, viscous oil | Links: @article{Losi_Arnone_Correra_Poesio_2016, title = {Modelling and statistical analysis of high viscosity oil/air slug flow characteristics in a small diameter horizontal pipe}, author = {Gianluca Losi and Davide Arnone and Sebastiano Correra and Pietro Poesio}, doi = {10.1016/j.ces.2016.04.005}, year = {2016}, date = {2016-07-12}, journal = {Chemical Engineering Science}, volume = {148}, pages = {190-202}, abstract = {High viscosity oil/air slug flow is investigated both experimentally and theoretically in this paper. The behaviour of three different oils, whose viscosities range from 0.037 Pa s to 0.804 Pa s, is investigated in a horizontal pipe with 0.022 m I.D. and 9 m length. A statistical approach is adopted during the tests so to collect a meaningful amount of data and to build the probability density functions for slug lengths. A new correlation to model the dependence from superficial gas velocity is introduced. The length correlation along with a corrected version of the Nicklin (1962) correlation are used as input into a developed mechanistic model, which is able to predict the pressure drops along the slug unit. The MTF model (Ullmann et al., 2006) is used as closure relation for shear stresses in the stratified region. The model is validated against the pressure drops obtained from performed experiments showing good capabilities and providing detailed pieces of information about the mechanics of the flow regime.}, keywords = {Pressure drops, Slug flow, slug flow model, slug lengths, viscous oil}, pubstate = {published}, tppubtype = {article} } High viscosity oil/air slug flow is investigated both experimentally and theoretically in this paper. The behaviour of three different oils, whose viscosities range from 0.037 Pa s to 0.804 Pa s, is investigated in a horizontal pipe with 0.022 m I.D. and 9 m length. A statistical approach is adopted during the tests so to collect a meaningful amount of data and to build the probability density functions for slug lengths. A new correlation to model the dependence from superficial gas velocity is introduced. The length correlation along with a corrected version of the Nicklin (1962) correlation are used as input into a developed mechanistic model, which is able to predict the pressure drops along the slug unit. The MTF model (Ullmann et al., 2006) is used as closure relation for shear stresses in the stratified region. The model is validated against the pressure drops obtained from performed experiments showing good capabilities and providing detailed pieces of information about the mechanics of the flow regime. | |

92. | Losi, Gianluca; Poesio, Pietro An experimental investigation on the effect of viscosity on bubbles moving in horizontal and slightly inclined pipes Journal Article Experimental Thermal and Fluid Science, 75 , pp. 77-88, 2016. Abstract | BibTeX | Tags: Benjamin bubble, Drift velocity, Highly viscous oil | Links: @article{Losi_Poesio_2016, title = {An experimental investigation on the effect of viscosity on bubbles moving in horizontal and slightly inclined pipes}, author = {Gianluca Losi and Pietro Poesio}, doi = {10.1016/j.expthermflusci.2016.01.010}, year = {2016}, date = {2016-07-01}, journal = {Experimental Thermal and Fluid Science}, volume = {75}, pages = {77-88}, abstract = {The motion of long bubbles in horizontal and slightly inclined pipes is a thoroughly investigated phenomenon. However, few results are available in literature for the drift velocity of a gas bubble in viscous liquids. The aim of this study is to experimentally analyse the effect of viscosity on the drift velocity of an air bubble in horizontal and inclined pipes. Two different measurement techniques are used: five capacitance probes are placed along the pipe to monitor the velocity evolution and image analysis is used to measure the bubble front velocity at two different distances from the outlet. The results of the measurements show that for horizontal case, as opposite to Benjamin (1968), the bubble drift velocity is not constant while the front displaces along the pipe and, in general, the viscosity slows down the propagation rate of the bubble. Finally, two drift velocity closure equations are tested with collected data.}, keywords = {Benjamin bubble, Drift velocity, Highly viscous oil}, pubstate = {published}, tppubtype = {article} } The motion of long bubbles in horizontal and slightly inclined pipes is a thoroughly investigated phenomenon. However, few results are available in literature for the drift velocity of a gas bubble in viscous liquids. The aim of this study is to experimentally analyse the effect of viscosity on the drift velocity of an air bubble in horizontal and inclined pipes. Two different measurement techniques are used: five capacitance probes are placed along the pipe to monitor the velocity evolution and image analysis is used to measure the bubble front velocity at two different distances from the outlet. The results of the measurements show that for horizontal case, as opposite to Benjamin (1968), the bubble drift velocity is not constant while the front displaces along the pipe and, in general, the viscosity slows down the propagation rate of the bubble. Finally, two drift velocity closure equations are tested with collected data. | |

91. | Beretta, Gian Paolo; Janbozorgi, Mohammad; Metghalchi, Hameed Degree of Disequilibrium analysis for automatic selection of kinetic constraints in the Rate-Controlled Constrained-Equilibrium method Journal Article Combustion and Flame, 168 , pp. 342-364, 2016. Abstract | BibTeX | Tags: chemical relaxation, Model order reduction in chemical kinetics, Non-equilibrium thermodynamics, rate-controlled constrained-equilibrium (RCCE) method | Links: @article{Beretta_Janbozorgi_2016, title = {Degree of Disequilibrium analysis for automatic selection of kinetic constraints in the Rate-Controlled Constrained-Equilibrium method}, author = {Gian Paolo Beretta and Mohammad Janbozorgi and Hameed Metghalchi}, doi = {10.1016/j.combustflame.2016.02.005}, year = {2016}, date = {2016-06-01}, journal = {Combustion and Flame}, volume = {168}, pages = {342-364}, abstract = {The Rate-Controlled Constrained-Equilibrium (RCCE) model reduction scheme for chemical kinetics provides acceptable accuracies with a number of differential equations much lower than the number of species in the underlying Detailed Kinetic Model (DKM). To yield good approximations, however, the method requires accurate identification of the rate controlling constraints. So far, a drawback of the RCCE scheme has been the absence of a fully automatable and systematic procedure that is capable of identifying the best constraints for a given range of thermodynamic conditions and a required level of approximation. In this paper, we propose a new methodology for such identification based on a simple algebraic analysis of the results of a preliminary simulation of the underlying DKM, which is focused on the behaviour of the degrees of disequilibrium (DoD) of the individual chemical reactions. The new methodology is based on computing an Approximate Reduced Row Echelon Form of the Actual Degrees of Disequilibrium (ARREFADD) with respect to a preset tolerance level. An alternative variant is to select an Approximate Singular Value Decomposition of the Actual Degrees of Disequilibrium (ASVDADD). Either procedure identifies a low dimensional subspace in the DoD space, from which the actual DoD traces do not depart beyond a fixed distance related to the preset tolerance (ARREFADD methodology) or to the first neglected singular value of the matrix of DoD traces (ASVDADD methodology). The effectiveness and robustness of the method is demonstrated for the case of a very rapid supersonic nozzle expansion of the products of hydrogen and methane oxycombustion and for the case of methane/oxygen ignition. The results are in excellent agreement with DKM predictions. For both variants of the method, we provide a simple Matlab code implementing the proposed constraint selection algorithm.}, keywords = {chemical relaxation, Model order reduction in chemical kinetics, Non-equilibrium thermodynamics, rate-controlled constrained-equilibrium (RCCE) method}, pubstate = {published}, tppubtype = {article} } The Rate-Controlled Constrained-Equilibrium (RCCE) model reduction scheme for chemical kinetics provides acceptable accuracies with a number of differential equations much lower than the number of species in the underlying Detailed Kinetic Model (DKM). To yield good approximations, however, the method requires accurate identification of the rate controlling constraints. So far, a drawback of the RCCE scheme has been the absence of a fully automatable and systematic procedure that is capable of identifying the best constraints for a given range of thermodynamic conditions and a required level of approximation. In this paper, we propose a new methodology for such identification based on a simple algebraic analysis of the results of a preliminary simulation of the underlying DKM, which is focused on the behaviour of the degrees of disequilibrium (DoD) of the individual chemical reactions. The new methodology is based on computing an Approximate Reduced Row Echelon Form of the Actual Degrees of Disequilibrium (ARREFADD) with respect to a preset tolerance level. An alternative variant is to select an Approximate Singular Value Decomposition of the Actual Degrees of Disequilibrium (ASVDADD). Either procedure identifies a low dimensional subspace in the DoD space, from which the actual DoD traces do not depart beyond a fixed distance related to the preset tolerance (ARREFADD methodology) or to the first neglected singular value of the matrix of DoD traces (ASVDADD methodology). The effectiveness and robustness of the method is demonstrated for the case of a very rapid supersonic nozzle expansion of the products of hydrogen and methane oxycombustion and for the case of methane/oxygen ignition. The results are in excellent agreement with DKM predictions. For both variants of the method, we provide a simple Matlab code implementing the proposed constraint selection algorithm. | |

90. | Gordiychuk, Andriy; Svanera, Michele; Benini, Sergio; Poesio, Pietro Size distribution and Sauter mean diameter of micro bubbles for a Venturi type bubble generator Journal Article Experimental Thermal and Fluid Science, 70 , pp. 51-60, 2016. Abstract | BibTeX | Tags: Bubble generator, Bubble size distribution, Micro bubbles | Links: @article{Gordiychuk_2016, title = {Size distribution and Sauter mean diameter of micro bubbles for a Venturi type bubble generator}, author = {Andriy Gordiychuk and Michele Svanera and Sergio Benini and Pietro Poesio}, doi = {10.1016/j.expthermflusci.2015.08.014}, year = {2016}, date = {2016-01-01}, journal = {Experimental Thermal and Fluid Science}, volume = {70}, pages = {51-60}, abstract = {An investigation is carried out to determine how air and water flow rates as well as the air inlet size (variable parameters) influence the size distribution of micro bubbles for a Venturi type bubble generator. Size distribution is extracted from the videos captured during the experiments using two different post processing algorithms which all report similar trends. The significance of the size distribution of micro bubbles is discussed and the results of the experiments are reported. It is shown that Sauter mean diameter and statistical parameters of log-normal distribution are influenced by the variable parameters and can be expressed using theoretical model based on dimensionless numbers containing these parameters. It is shown that such theoretical model reports influence of variable parameters on the investigated ones which is consistent with the population balance model as well as with the correlations previously reported in literature. Finally, the significance of correlation between variable parameters and statistical parameters of the distribution is discussed.}, keywords = {Bubble generator, Bubble size distribution, Micro bubbles}, pubstate = {published}, tppubtype = {article} } An investigation is carried out to determine how air and water flow rates as well as the air inlet size (variable parameters) influence the size distribution of micro bubbles for a Venturi type bubble generator. Size distribution is extracted from the videos captured during the experiments using two different post processing algorithms which all report similar trends. The significance of the size distribution of micro bubbles is discussed and the results of the experiments are reported. It is shown that Sauter mean diameter and statistical parameters of log-normal distribution are influenced by the variable parameters and can be expressed using theoretical model based on dimensionless numbers containing these parameters. It is shown that such theoretical model reports influence of variable parameters on the investigated ones which is consistent with the population balance model as well as with the correlations previously reported in literature. Finally, the significance of correlation between variable parameters and statistical parameters of the distribution is discussed. | |

## 2015 |
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89. | Montefusco, Alberto; Consonni, Francesco; Beretta, Gian Paolo Essential equivalence of the general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) and steepest-entropy-ascent models of dissipation for nonequilibrium thermodynamics Journal Article Physical Review E, 91 (4), pp. 042138, 2015. Abstract | BibTeX | Tags: dissipation, GENERIC, steepest-entropy-ascent, thermodynamics | Links: @article{Montefusco_Consonni_Beretta_2015, title = {Essential equivalence of the general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) and steepest-entropy-ascent models of dissipation for nonequilibrium thermodynamics}, author = {Alberto Montefusco and Francesco Consonni and Gian Paolo Beretta}, doi = {10.1103/PhysRevE.91.042138}, year = {2015}, date = {2015-04-28}, journal = {Physical Review E}, volume = {91}, number = {4}, pages = {042138}, abstract = {By reformulating the steepest-entropy-ascent (SEA) dynamical model for nonequilibrium thermodynamics in the mathematical language of differential geometry, we compare it with the primitive formulation of the general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) model and discuss the main technical differences of the two approaches. In both dynamical models the description of dissipation is of the “entropy-gradient” type. SEA focuses only on the dissipative, i.e., entropy generating, component of the time evolution, chooses a sub-Riemannian metric tensor as dissipative structure, and uses the local entropy density field as potential. GENERIC emphasizes the coupling between the dissipative and nondissipative components of the time evolution, chooses two compatible degenerate structures (Poisson and degenerate co-Riemannian), and uses the global energy and entropy functionals as potentials. As an illustration, we rewrite the known GENERIC formulation of the Boltzmann equation in terms of the square root of the distribution function adopted by the SEA formulation. We then provide a formal proof that in more general frameworks, whenever all degeneracies in the GENERIC framework are related to conservation laws, the SEA and GENERIC models of the dissipative component of the dynamics are essentially interchangeable, provided of course they assume the same kinematics. As part of the discussion, we note that equipping the dissipative structure of GENERIC with the Leibniz identity makes it automatically SEA on metric leaves.}, keywords = {dissipation, GENERIC, steepest-entropy-ascent, thermodynamics}, pubstate = {published}, tppubtype = {article} } By reformulating the steepest-entropy-ascent (SEA) dynamical model for nonequilibrium thermodynamics in the mathematical language of differential geometry, we compare it with the primitive formulation of the general equation for the nonequilibrium reversible-irreversible coupling (GENERIC) model and discuss the main technical differences of the two approaches. In both dynamical models the description of dissipation is of the “entropy-gradient” type. SEA focuses only on the dissipative, i.e., entropy generating, component of the time evolution, chooses a sub-Riemannian metric tensor as dissipative structure, and uses the local entropy density field as potential. GENERIC emphasizes the coupling between the dissipative and nondissipative components of the time evolution, chooses two compatible degenerate structures (Poisson and degenerate co-Riemannian), and uses the global energy and entropy functionals as potentials. As an illustration, we rewrite the known GENERIC formulation of the Boltzmann equation in terms of the square root of the distribution function adopted by the SEA formulation. We then provide a formal proof that in more general frameworks, whenever all degeneracies in the GENERIC framework are related to conservation laws, the SEA and GENERIC models of the dissipative component of the dynamics are essentially interchangeable, provided of course they assume the same kinematics. As part of the discussion, we note that equipping the dissipative structure of GENERIC with the Leibniz identity makes it automatically SEA on metric leaves. | |

88. | Picchi, Davide; Manerba, Yuri; Correra, Sebastiano; Margarone, Michele; Poesio, Pietro Gas/shear-thinning liquid flows through pipes: Modeling and experiments Journal Article International Journal of Multiphase Flow, 73 , pp. 217-226, 2015. Abstract | BibTeX | Tags: Flow pattern maps, Pressure gradient, Shear-thinning fluid, Slug frequency, Slug velocity, Stratified flow | Links: @article{Picchi2015, title = {Gas/shear-thinning liquid flows through pipes: Modeling and experiments}, author = {Davide Picchi and Yuri Manerba and Sebastiano Correra and Michele Margarone and Pietro Poesio}, doi = {10.1016/j.ijmultiphaseflow.2015.03.005}, year = {2015}, date = {2015-03-21}, journal = {International Journal of Multiphase Flow}, volume = {73}, pages = {217-226}, abstract = {In chemical and oil industry gas/shear-thinning liquid two-phase flows are frequently encountered. In this work, we investigate experimentally the flow characteristics of air/shear-thinning liquid systems in horizontal and slightly inclined smooth pipes. The experiments are performed in a 9-m-long glass pipe using air and three different carboxymethyl cellulose (CMC) solutions as test fluids. Flow pattern maps are built by visual observation using a high-speed camera. The observed flow patterns are stratified, plug, and slug flow. The effects of the pipe inclination and the rheology of the shear-thinning fluid in terms of flow pattern maps are presented. The predicted existence region of the stratified flow regime is compared with the experimental observation showing a good agreement. A mechanistic model valid for air/power-law slug flow is proposed and model predictions are compared to the experimental data showing a good agreement. Slug flow characteristics are investigated by the analysis of the signals of a capacitance probe: slug velocity, slug frequency, and slug lengths are measured. A new correlation for the slug frequency is proposed and the results are promising.}, keywords = {Flow pattern maps, Pressure gradient, Shear-thinning fluid, Slug frequency, Slug velocity, Stratified flow}, pubstate = {published}, tppubtype = {article} } In chemical and oil industry gas/shear-thinning liquid two-phase flows are frequently encountered. In this work, we investigate experimentally the flow characteristics of air/shear-thinning liquid systems in horizontal and slightly inclined smooth pipes. The experiments are performed in a 9-m-long glass pipe using air and three different carboxymethyl cellulose (CMC) solutions as test fluids. Flow pattern maps are built by visual observation using a high-speed camera. The observed flow patterns are stratified, plug, and slug flow. The effects of the pipe inclination and the rheology of the shear-thinning fluid in terms of flow pattern maps are presented. The predicted existence region of the stratified flow regime is compared with the experimental observation showing a good agreement. A mechanistic model valid for air/power-law slug flow is proposed and model predictions are compared to the experimental data showing a good agreement. Slug flow characteristics are investigated by the analysis of the signals of a capacitance probe: slug velocity, slug frequency, and slug lengths are measured. A new correlation for the slug frequency is proposed and the results are promising. | |

87. | Beretta, Gian Paolo; Gyftopoulos, Elias A novel sequence of exposition of engineering thermodynamics Journal Article Journal of Energy Resources Technology, 137 (2), pp. 021009, 2015. Abstract | BibTeX | Tags: engineering thermodynamics | Links: @article{Beretta_Gyftopoulos_2015_1, title = {A novel sequence of exposition of engineering thermodynamics}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos}, doi = {10.1115/1.4026385}, year = {2015}, date = {2015-03-01}, journal = {Journal of Energy Resources Technology}, volume = {137}, number = {2}, pages = {021009}, abstract = {We present the foundations of thermodynamics in a novel sequence in which all basic concepts are defined in terms of well known mechanical ideas. Many definitions are new. The order of introduction of concepts is: system (constituents and parameters); properties; state; energy (without heat and work) and energy balance; classification of states in terms of time evolution; existence of stable equilibrium states; available energy; entropy (without heat and temperature) of any state (equilibrium or not) and entropy balance; properties of stable equilibrium states; temperature in terms of energy and entropy; chemical potentials; pressure; work; heat; applications of balances. This novel sequence not only generalizes the subject of thermodynamics to all systems (large or small) and all states (equilibrium and not equilibrium) but also avoids both the conceptual and definitional difficulties that have been recognized by so many teachers, and the confusion experienced by so many students.}, keywords = {engineering thermodynamics}, pubstate = {published}, tppubtype = {article} } We present the foundations of thermodynamics in a novel sequence in which all basic concepts are defined in terms of well known mechanical ideas. Many definitions are new. The order of introduction of concepts is: system (constituents and parameters); properties; state; energy (without heat and work) and energy balance; classification of states in terms of time evolution; existence of stable equilibrium states; available energy; entropy (without heat and temperature) of any state (equilibrium or not) and entropy balance; properties of stable equilibrium states; temperature in terms of energy and entropy; chemical potentials; pressure; work; heat; applications of balances. This novel sequence not only generalizes the subject of thermodynamics to all systems (large or small) and all states (equilibrium and not equilibrium) but also avoids both the conceptual and definitional difficulties that have been recognized by so many teachers, and the confusion experienced by so many students. | |

86. | Beretta, Gian Paolo; Gyftopoulos, Elias What is a chemical equilibrium state? Journal Article Journal of Energy Resources Technology, 137 (2), pp. 021008, 2015. Abstract | BibTeX | Tags: chemical equilibrium state | Links: @article{Beretta_Gyftopoulos_2015_2, title = {What is a chemical equilibrium state?}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos}, doi = {10.1115/1.4026384}, year = {2015}, date = {2015-03-01}, journal = {Journal of Energy Resources Technology}, volume = {137}, number = {2}, pages = {021008}, abstract = {We review the chemical equilibrium equations, and conclude that both their derivation and their meaning are problematic. We find that these equations can be established for a suitably defined simple system without chemical reactions.}, keywords = {chemical equilibrium state}, pubstate = {published}, tppubtype = {article} } We review the chemical equilibrium equations, and conclude that both their derivation and their meaning are problematic. We find that these equations can be established for a suitably defined simple system without chemical reactions. | |

85. | Beretta, Gian Paolo; Gyftopoulos, Elias What is a simple system? Journal Article Journal of Energy Resources Technology, 137 (2), pp. 021007, 2015. Abstract | BibTeX | Tags: simple system | Links: @article{Beretta_Gyftopoulos_2015_3, title = {What is a simple system?}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos}, doi = {10.1115/1.4026383}, year = {2015}, date = {2015-03-01}, journal = {Journal of Energy Resources Technology}, volume = {137}, number = {2}, pages = {021007}, abstract = {We discuss relations among properties of systems that consist of any amounts of constituents (including one particle), that have volume as the only parameter, and that are in thermodynamic equilibrium or stable equilibrium states. For large amounts of constituents, we introduce the concept of a simple system, and derive additional relations among properties.}, keywords = {simple system}, pubstate = {published}, tppubtype = {article} } We discuss relations among properties of systems that consist of any amounts of constituents (including one particle), that have volume as the only parameter, and that are in thermodynamic equilibrium or stable equilibrium states. For large amounts of constituents, we introduce the concept of a simple system, and derive additional relations among properties. | |

84. | Beretta, Gian Paolo; Gyftopoulos, Elias What is heat? Journal Article Journal of Energy Resources Technology, 137 (2), pp. 021006, 2015. Abstract | BibTeX | Tags: heat | Links: @article{Beretta_Gyftopoulos_2015_4, title = {What is heat?}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos}, doi = {10.1115/1.4026382}, year = {2015}, date = {2015-03-01}, journal = {Journal of Energy Resources Technology}, volume = {137}, number = {2}, pages = {021006}, abstract = {We define heat as a particular kind of nonwork interaction that involves only energy and entropy transfers, and that is entirely distinguishable from work. The existence of heat interactions is a consequence of the first and second laws of thermodynamics. The requirement that heat be entirely distinguishable from work implies strict conditions on the end states of the interacting systems, and guarantees a definite relation between such states and the energy and entropy transfers. We illustrate these conditions by using energy versus entropy graphs. Many experiences can be represented as heat interactions, including the exchanges between two black bodies at temperatures that differ infinitesimally. We discuss the latter point in a companion paper at this conference.}, keywords = {heat}, pubstate = {published}, tppubtype = {article} } We define heat as a particular kind of nonwork interaction that involves only energy and entropy transfers, and that is entirely distinguishable from work. The existence of heat interactions is a consequence of the first and second laws of thermodynamics. The requirement that heat be entirely distinguishable from work implies strict conditions on the end states of the interacting systems, and guarantees a definite relation between such states and the energy and entropy transfers. We illustrate these conditions by using energy versus entropy graphs. Many experiences can be represented as heat interactions, including the exchanges between two black bodies at temperatures that differ infinitesimally. We discuss the latter point in a companion paper at this conference. | |

83. | Beretta, Gian Paolo; Gyftopoulos, Elias Electromagnetic radiation: a carrier of energy and entropy Journal Article Journal of Energy Resources Technology, 137 (2), pp. 021005, 2015. Abstract | BibTeX | Tags: electromagnetic radiation, energy, entropy | Links: @article{Beretta_Gyftopoulos_2015_5, title = {Electromagnetic radiation: a carrier of energy and entropy}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos}, doi = {10.1115/1.4026381}, year = {2015}, date = {2015-03-01}, journal = {Journal of Energy Resources Technology}, volume = {137}, number = {2}, pages = {021005}, abstract = {Starting from the properties of the electromagnetic radiation field at stable equilibrium, we derive expressions for the flows of energy and entropy between two black bodies at different temperatures, interacting only through electromagnetic radiation. We find that in general the interaction through radiation is nonwork but not heat. It is heat only if the temperature difference between the interacting systems is infinitesimal.}, keywords = {electromagnetic radiation, energy, entropy}, pubstate = {published}, tppubtype = {article} } Starting from the properties of the electromagnetic radiation field at stable equilibrium, we derive expressions for the flows of energy and entropy between two black bodies at different temperatures, interacting only through electromagnetic radiation. We find that in general the interaction through radiation is nonwork but not heat. It is heat only if the temperature difference between the interacting systems is infinitesimal. | |

82. | Beretta, Gian Paolo; Gyftopoulos, Elias What is the third law? Journal Article Journal of Energy Resources Technology, 137 (2), pp. 021004, 2015. Abstract | BibTeX | Tags: third law | Links: @article{Beretta_Gyftopoulos_2015_6, title = {What is the third law?}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos}, doi = {10.1115/1.4026380}, year = {2015}, date = {2015-03-01}, journal = {Journal of Energy Resources Technology}, volume = {137}, number = {2}, pages = {021004}, abstract = {We discuss entropies of systems at very low temperatures or, equivalently, the third law of thermodynamics. We conclude that definitive values of such entropies can be established only by experiments on systems with very few degrees of freedom, such as one-particle systems.}, keywords = {third law}, pubstate = {published}, tppubtype = {article} } We discuss entropies of systems at very low temperatures or, equivalently, the third law of thermodynamics. We conclude that definitive values of such entropies can be established only by experiments on systems with very few degrees of freedom, such as one-particle systems. | |

81. | Beretta, Gian Paolo; Gyftopoulos, Elias What is the second law? Journal Article Journal of Energy Resources Technology, 137 (2), pp. 021003, 2015. Abstract | BibTeX | Tags: second law | Links: @article{Beretta_Gyftopoulos_2014_7, title = {What is the second law?}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos}, doi = {10.1115/1.4026379}, year = {2015}, date = {2015-03-01}, journal = {Journal of Energy Resources Technology}, volume = {137}, number = {2}, pages = {021003}, abstract = {The thesis of this article is that thermodynamics is a rigorous science, and that the first law and the second law can be stated in an unambiguous and general way so that their implications are concrete and valid for both equilibrium and nonequilibrium states. In this light, we summarize the principles of thermodynamics, and introduce a graphical tool, the energy versus entropy diagram, that is very helpful to explain and grasp the general implications of these principles, especially in the nonequilibrium domain.}, keywords = {second law}, pubstate = {published}, tppubtype = {article} } The thesis of this article is that thermodynamics is a rigorous science, and that the first law and the second law can be stated in an unambiguous and general way so that their implications are concrete and valid for both equilibrium and nonequilibrium states. In this light, we summarize the principles of thermodynamics, and introduce a graphical tool, the energy versus entropy diagram, that is very helpful to explain and grasp the general implications of these principles, especially in the nonequilibrium domain. | |

80. | Cano-Andrade, Sergio; Beretta, Gian Paolo; von Spakovsky, Michael Steepest-entropy-ascent quantum thermodynamic modeling of decoherence in two different microscopic composite systems Journal Article Physical Review A, 91 (1), pp. 013848, 2015. Abstract | BibTeX | Tags: decoherence, microscopic composite systems, quantum thermodinamics, steepest-entropy-ascent | Links: @article{Cano_Beretta_2015, title = {Steepest-entropy-ascent quantum thermodynamic modeling of decoherence in two different microscopic composite systems}, author = {Sergio Cano-Andrade and Gian Paolo Beretta and Michael R. von Spakovsky}, doi = {10.1103/PhysRevA.91.013848}, year = {2015}, date = {2015-01-30}, journal = {Physical Review A}, volume = {91}, number = {1}, pages = {013848}, abstract = {The steepest-entropy-ascent quantum thermodynamic (SEAQT) framework is used to model the decoherence that occurs during the state evolution of two different microscopic composite systems. The test cases are a two−spin−1/2−particle composite system and a particle-photon field composite system like that experimentally studied in cavity quantum electrodynamics. The first system is used to study the characteristics of the nonlinear equation of motion of the SEAQT framework when modeling the state evolution of a microscopic composite system with particular interest in the phenomenon of decoherence. The second system is used to compare the numerical predictions of the SEAQT framework with experimental cavity quantum electrodynamic data available in the literature. For the two different numerical cases presented, the time evolution of the density operator of the composite system as well as that of the reduced operators belonging to the two constituents is traced from an initial nonequilibrium state of the composite along its relaxation towards stable equilibrium. Results show for both cases how the initial entanglement and coherence is dissipated during the state relaxation towards a state of stable equilibrium.}, keywords = {decoherence, microscopic composite systems, quantum thermodinamics, steepest-entropy-ascent}, pubstate = {published}, tppubtype = {article} } The steepest-entropy-ascent quantum thermodynamic (SEAQT) framework is used to model the decoherence that occurs during the state evolution of two different microscopic composite systems. The test cases are a two−spin−1/2−particle composite system and a particle-photon field composite system like that experimentally studied in cavity quantum electrodynamics. The first system is used to study the characteristics of the nonlinear equation of motion of the SEAQT framework when modeling the state evolution of a microscopic composite system with particular interest in the phenomenon of decoherence. The second system is used to compare the numerical predictions of the SEAQT framework with experimental cavity quantum electrodynamic data available in the literature. For the two different numerical cases presented, the time evolution of the density operator of the composite system as well as that of the reduced operators belonging to the two constituents is traced from an initial nonequilibrium state of the composite along its relaxation towards stable equilibrium. Results show for both cases how the initial entanglement and coherence is dissipated during the state relaxation towards a state of stable equilibrium. | |

79. | Picchi, Davide; Strazza, Domenico; Demori, Marco; Ferrari, Vittorio; Poesio, Pietro An experimental investigation and two-fluid model validation for dilute viscous oil in water dispersed pipe flow Journal Article Experimental Thermal and Fluid Science, 60 , pp. 28-34, 2015. Abstract | BibTeX | Tags: Capacitance sensor, Hold-up, Oil in water dispersion, Pressure gradient, Slip ratio | Links: @article{Picchi_Strazza_2015, title = {An experimental investigation and two-fluid model validation for dilute viscous oil in water dispersed pipe flow}, author = {Davide Picchi and Domenico Strazza and Marco Demori and Vittorio Ferrari and Pietro Poesio}, doi = {10.1016/j.expthermflusci.2014.07.016}, year = {2015}, date = {2015-01-01}, journal = {Experimental Thermal and Fluid Science}, volume = {60}, pages = {28-34}, abstract = {In this work we investigated high viscous oil in water dispersions (Do/w) in pipe. The experiments are performed in a 22.8-mm-id 9-m-long horizontal glass pipe using a high viscous oil (density of 886 kg/m3 and viscosity of 900 mPa s) and tap water as test fluids. Pressure gradients are collected; hold-up data are measured using the quick-closing-valves technique (QCV) and a capacitance sensor, specifically optimized for dispersed flows detection. A new two-fluid model for liquid–liquid dispersed pipe flow to predict hold-up, pressure gradient, and the slip ratio between the liquid phases is presented. The experimental data are compared at first with homogeneous model predictions. Then the presented two-fluid model is validated against experimental data of this work and against experimental data taken from the literature showing a good agreement. The predicted and measured slip ratio is grater than unity for all oil–water dispersions investigated.}, keywords = {Capacitance sensor, Hold-up, Oil in water dispersion, Pressure gradient, Slip ratio}, pubstate = {published}, tppubtype = {article} } In this work we investigated high viscous oil in water dispersions (Do/w) in pipe. The experiments are performed in a 22.8-mm-id 9-m-long horizontal glass pipe using a high viscous oil (density of 886 kg/m3 and viscosity of 900 mPa s) and tap water as test fluids. Pressure gradients are collected; hold-up data are measured using the quick-closing-valves technique (QCV) and a capacitance sensor, specifically optimized for dispersed flows detection. A new two-fluid model for liquid–liquid dispersed pipe flow to predict hold-up, pressure gradient, and the slip ratio between the liquid phases is presented. The experimental data are compared at first with homogeneous model predictions. Then the presented two-fluid model is validated against experimental data of this work and against experimental data taken from the literature showing a good agreement. The predicted and measured slip ratio is grater than unity for all oil–water dispersions investigated. | |

78. | Ullmann, Amos; Poesio, Pietro; Brauner, Neima Enhancing heat transfer rates by inducing liquidliquid phase separation: Applications and modelling Journal Article Interfacial Phenomena and Heat Transfer, 3 (1), pp. 41-67, 2015. Abstract | BibTeX | Tags: convective heat transfer, Heat transfer enhancement, phase separation, Spinodal decomposition | Links: @article{Ullmann_Poesio_2015, title = {Enhancing heat transfer rates by inducing liquidliquid phase separation: Applications and modelling}, author = {Amos Ullmann and Pietro Poesio and Neima Brauner}, doi = {10.1615/InterfacPhenomHeatTransfer.2015012506 }, year = {2015}, date = {2015-01-01}, journal = {Interfacial Phenomena and Heat Transfer}, volume = {3}, number = {1}, pages = {41-67}, abstract = {This paper focuses on heat transfer enhancement during spinodal decomposition, and it provides an updated review as well as a discussion of future developments. The analysis is mainly based on the work of two research groups at Tel-Aviv University (Israel) and at University of Brescia (Italy). We review the theory of spinodal decomposition of liquid−liquid binary mixtures and we discuss the diffuse interface (DI) approach. While mass and momentum equations in the DI approach have been developed and discussed in other works, we also look into the energy equation, which has been only recently investigated. Direct visualizations of both static and flowing mixture during decomposition are provided. Visualizations of the decomposition in a quiescent fluid have been previously reported, while flowing conditions have been analyzed only recently. Interestingly enough, the morphology is rather different during flowing conditions, where the decomposition exhibits a nucleationlike morphology and not the typical bicontinuous structure observed during spinodal decomposition of a quiescent fluid. Enhancement of heat transfer performances is shown in channels (sizes of 0.8 and 2 mm) using an upper critical solution temperature (UCST) mixture. Although different conditions are analyzed, the results show a consistent enhancement of the heat transfer. The paper reports also some new experimental work on the heat transfer for a lower critical solution temperature (LCST) mixture that can be actually used in cooling applications. A coarse-grained model that could be potentially used for the sizing of large-scale equipment is discussed in term of a possible future development that needs to be further investigated and validated.}, keywords = {convective heat transfer, Heat transfer enhancement, phase separation, Spinodal decomposition}, pubstate = {published}, tppubtype = {article} } This paper focuses on heat transfer enhancement during spinodal decomposition, and it provides an updated review as well as a discussion of future developments. The analysis is mainly based on the work of two research groups at Tel-Aviv University (Israel) and at University of Brescia (Italy). We review the theory of spinodal decomposition of liquid−liquid binary mixtures and we discuss the diffuse interface (DI) approach. While mass and momentum equations in the DI approach have been developed and discussed in other works, we also look into the energy equation, which has been only recently investigated. Direct visualizations of both static and flowing mixture during decomposition are provided. Visualizations of the decomposition in a quiescent fluid have been previously reported, while flowing conditions have been analyzed only recently. Interestingly enough, the morphology is rather different during flowing conditions, where the decomposition exhibits a nucleationlike morphology and not the typical bicontinuous structure observed during spinodal decomposition of a quiescent fluid. Enhancement of heat transfer performances is shown in channels (sizes of 0.8 and 2 mm) using an upper critical solution temperature (UCST) mixture. Although different conditions are analyzed, the results show a consistent enhancement of the heat transfer. The paper reports also some new experimental work on the heat transfer for a lower critical solution temperature (LCST) mixture that can be actually used in cooling applications. A coarse-grained model that could be potentially used for the sizing of large-scale equipment is discussed in term of a possible future development that needs to be further investigated and validated. | |

## 2014 |
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77. | Beretta, Gian Paolo; Iora, Paolo; Ghoniem, Ahmed Allocating resources and products in multi-hybrid multi-cogeneration: What fractions of heat and power are renewable in hybrid fossil-solar CHP? Journal Article Energy, 78 , pp. 587-603, 2014. Abstract | BibTeX | Tags: hybrid fossil-solar CHP, multi-cogeration, renewable | Links: @article{Beretta_Iora_2014, title = {Allocating resources and products in multi-hybrid multi-cogeneration: What fractions of heat and power are renewable in hybrid fossil-solar CHP?}, author = {Gian Paolo Beretta and Paolo Iora and Ahmed F. Ghoniem}, doi = {10.1016/j.energy.2014.10.046}, year = {2014}, date = {2014-12-15}, journal = {Energy}, volume = {78}, pages = {587-603}, abstract = {A general method for the allocation of resources and products in multi-resource/multi-product facilities is developed with particular reference to the important two-resource/two-product case of hybrid fossil & solar/heat & power cogeneration. For a realistic case study, we show how the method allows to assess what fractions of the power and heat should be considered as produced from the solar resource and hence identified as renewable. In the present scenario where the hybridization of fossil power plants by solar-integration is gaining increasing attention, such assessment is of great importance in the fair and balanced development of local energy policies based on granting incentives to renewables resources. The paper extends to the case of two-resource/two-product hybrid cogeneration, as well as to general multi-resource/multi-generation, three of the allocation methods already available for single-resource/two-product cogeneration and for two-resource/single-product hybrid facilities, namely, the ExRR (Exergy-based Reversible-Reference) method, the SRSPR (Single Resource Separate Production Reference) method, and the STALPR (Self-Tuned-Average-Local-Productions-Reference) method. For the case study considered we show that, unless the SRSPR reference efficiencies are constantly updated, the differences between the STALPR and SRSPR methods become important as hybrid and cogeneration plants take up large shares of the local energy production portfolio.}, keywords = {hybrid fossil-solar CHP, multi-cogeration, renewable}, pubstate = {published}, tppubtype = {article} } A general method for the allocation of resources and products in multi-resource/multi-product facilities is developed with particular reference to the important two-resource/two-product case of hybrid fossil & solar/heat & power cogeneration. For a realistic case study, we show how the method allows to assess what fractions of the power and heat should be considered as produced from the solar resource and hence identified as renewable. In the present scenario where the hybridization of fossil power plants by solar-integration is gaining increasing attention, such assessment is of great importance in the fair and balanced development of local energy policies based on granting incentives to renewables resources. The paper extends to the case of two-resource/two-product hybrid cogeneration, as well as to general multi-resource/multi-generation, three of the allocation methods already available for single-resource/two-product cogeneration and for two-resource/single-product hybrid facilities, namely, the ExRR (Exergy-based Reversible-Reference) method, the SRSPR (Single Resource Separate Production Reference) method, and the STALPR (Self-Tuned-Average-Local-Productions-Reference) method. For the case study considered we show that, unless the SRSPR reference efficiencies are constantly updated, the differences between the STALPR and SRSPR methods become important as hybrid and cogeneration plants take up large shares of the local energy production portfolio. | |

76. | Demori, Marco; Ferrari,; Ferrari, Vittorio; Farisè, Stefano; Poesio, Pietro Energy harvesting from von Karman vortices in airflow for autonomous sensors Journal Article Procedia Engineering - EUROSENSORS 2014, the 28th European Conference on Solid-State Transducers, 87 , pp. 775-778, 2014. Abstract | BibTeX | Tags: autonomous sensors, Piezoeletric energy harvesting, Von Karman vortices | Links: @article{Demori_Ferrari_2014, title = {Energy harvesting from von Karman vortices in airflow for autonomous sensors}, author = {Marco Demori and M. Ferrari and Vittorio Ferrari and Stefano Farisè and Pietro Poesio}, doi = {10.1016/j.proeng.2014.11.655}, year = {2014}, date = {2014-12-01}, journal = {Procedia Engineering - EUROSENSORS 2014, the 28th European Conference on Solid-State Transducers}, volume = {87}, pages = {775-778}, abstract = {In this paper an innovative energy harvesting system based on a piezoelectric converter to extract energy from airflow and use it to power autonomous sensors is presented. The converter is embedded as a part of a flexure beam that is put into vibrations by Von Karman vortices detached from a bluff body placed upstream. The results of experimental characterization show that higher conversion effectiveness is obtained for flow velocities where the frequency of the vortices matches the resonant frequency corresponding to the first flexural mode of the beam. The possibility to power autonomous sensors has been shown by developing an energy management and signal conditioning electronic circuit plus two sensors for the transmission of a RF signal from which temperature and flow velocity can be extracted. A harvested power of about 100 μW with retransmission intervals below 2 min have been obtained.}, keywords = {autonomous sensors, Piezoeletric energy harvesting, Von Karman vortices}, pubstate = {published}, tppubtype = {article} } In this paper an innovative energy harvesting system based on a piezoelectric converter to extract energy from airflow and use it to power autonomous sensors is presented. The converter is embedded as a part of a flexure beam that is put into vibrations by Von Karman vortices detached from a bluff body placed upstream. The results of experimental characterization show that higher conversion effectiveness is obtained for flow velocities where the frequency of the vortices matches the resonant frequency corresponding to the first flexural mode of the beam. The possibility to power autonomous sensors has been shown by developing an energy management and signal conditioning electronic circuit plus two sensors for the transmission of a RF signal from which temperature and flow velocity can be extracted. A harvested power of about 100 μW with retransmission intervals below 2 min have been obtained. | |

75. | Beretta, Gian Paolo Steepest entropy ascent model for far-nonequilibrium thermodynamics: Unified implementation of the maximum entropy production principle Journal Article Physical Review E, 90 (4), pp. 042113, 2014. Abstract | BibTeX | Tags: entropy, nonequilibrium states, steepest-entropy-ascent | Links: @article{Beretta_2014, title = {Steepest entropy ascent model for far-nonequilibrium thermodynamics: Unified implementation of the maximum entropy production principle}, author = {Gian Paolo Beretta}, doi = {10.1103/PhysRevE.90.042113}, year = {2014}, date = {2014-10-07}, journal = {Physical Review E}, volume = {90}, number = {4}, pages = {042113}, abstract = {By suitable reformulations, we cast the mathematical frameworks of several well-known different approaches to the description of nonequilibrium dynamics into a unified formulation valid in all these contexts, which extends to such frameworks the concept of steepest entropy ascent (SEA) dynamics introduced by the present author in previous works on quantum thermodynamics. Actually, the present formulation constitutes a generalization also for the quantum thermodynamics framework. The analysis emphasizes that in the SEA modeling principle a key role is played by the geometrical metric with respect to which to measure the length of a trajectory in state space. In the near-thermodynamic-equilibrium limit, the metric tensor is directly related to the Onsager's generalized resistivity tensor. Therefore, through the identification of a suitable metric field which generalizes the Onsager generalized resistance to the arbitrarily far-nonequilibrium domain, most of the existing theories of nonequilibrium thermodynamics can be cast in such a way that the state exhibits the spontaneous tendency to evolve in state space along the path of SEA compatible with the conservation constraints and the boundary conditions. The resulting unified family of SEA dynamical models is intrinsically and strongly consistent with the second law of thermodynamics. The non-negativity of the entropy production is a general and readily proved feature of SEA dynamics. In several of the different approaches to nonequilibrium description we consider here, the SEA concept has not been investigated before. We believe it defines the precise meaning and the domain of general validity of the so-called maximum entropy production principle. Therefore, it is hoped that the present unifying approach may prove useful in providing a fresh basis for effective, thermodynamically consistent, numerical models and theoretical treatments of irreversible conservative relaxation towards equilibrium from far nonequilibrium states. The mathematical frameworks we consider are the following: (A) statistical or information-theoretic models of relaxation; (B) small-scale and rarefied gas dynamics (i.e., kinetic models for the Boltzmann equation); (C) rational extended thermodynamics, macroscopic nonequilibrium thermodynamics, and chemical kinetics; (D) mesoscopic nonequilibrium thermodynamics, continuum mechanics with fluctuations; and (E) quantum statistical mechanics, quantum thermodynamics, mesoscopic nonequilibrium quantum thermodynamics, and intrinsic quantum thermodynamics.}, keywords = {entropy, nonequilibrium states, steepest-entropy-ascent}, pubstate = {published}, tppubtype = {article} } By suitable reformulations, we cast the mathematical frameworks of several well-known different approaches to the description of nonequilibrium dynamics into a unified formulation valid in all these contexts, which extends to such frameworks the concept of steepest entropy ascent (SEA) dynamics introduced by the present author in previous works on quantum thermodynamics. Actually, the present formulation constitutes a generalization also for the quantum thermodynamics framework. The analysis emphasizes that in the SEA modeling principle a key role is played by the geometrical metric with respect to which to measure the length of a trajectory in state space. In the near-thermodynamic-equilibrium limit, the metric tensor is directly related to the Onsager's generalized resistivity tensor. Therefore, through the identification of a suitable metric field which generalizes the Onsager generalized resistance to the arbitrarily far-nonequilibrium domain, most of the existing theories of nonequilibrium thermodynamics can be cast in such a way that the state exhibits the spontaneous tendency to evolve in state space along the path of SEA compatible with the conservation constraints and the boundary conditions. The resulting unified family of SEA dynamical models is intrinsically and strongly consistent with the second law of thermodynamics. The non-negativity of the entropy production is a general and readily proved feature of SEA dynamics. In several of the different approaches to nonequilibrium description we consider here, the SEA concept has not been investigated before. We believe it defines the precise meaning and the domain of general validity of the so-called maximum entropy production principle. Therefore, it is hoped that the present unifying approach may prove useful in providing a fresh basis for effective, thermodynamically consistent, numerical models and theoretical treatments of irreversible conservative relaxation towards equilibrium from far nonequilibrium states. The mathematical frameworks we consider are the following: (A) statistical or information-theoretic models of relaxation; (B) small-scale and rarefied gas dynamics (i.e., kinetic models for the Boltzmann equation); (C) rational extended thermodynamics, macroscopic nonequilibrium thermodynamics, and chemical kinetics; (D) mesoscopic nonequilibrium thermodynamics, continuum mechanics with fluctuations; and (E) quantum statistical mechanics, quantum thermodynamics, mesoscopic nonequilibrium quantum thermodynamics, and intrinsic quantum thermodynamics. | |

74. | Poesio, Pietro; Wang, Evelyn Resonance induced wetting state transition of a ferrofluid droplet on superhydrophobic surfaces Journal Article Experimental Thermal and Fluid Science, 57 , pp. 353-357, 2014. Abstract | BibTeX | Tags: Ferrofluid, Superhydrophobic surface, Wetting transition | Links: @article{Poesio_Wang_2014, title = {Resonance induced wetting state transition of a ferrofluid droplet on superhydrophobic surfaces}, author = {Pietro Poesio and Evelyn N. Wang}, doi = {10.1016/j.expthermflusci.2014.02.012}, year = {2014}, date = {2014-06-09}, journal = {Experimental Thermal and Fluid Science}, volume = {57}, pages = {353-357}, abstract = {We investigated manipulating wetting transitions of ferrofluid droplets on planar superhydrophobic surfaces by electromagnetic stimulation. We showed that even if magnetic forces are small at small liquid volumes (1–10 μl), they can be effectively used to induce Cassie to Wenzel transition when the exciting frequency is close to the resonant frequency. We related the wetting transition to the increase of the Laplace pressure as a consequence of the large deformation that occurs close to the resonant frequency; on the contrary, inertia forces were not able to induce such a transition. This study promises a new approach to manipulate ferrofluid droplets for various microfluidic and lab-on-chip technologies.}, keywords = {Ferrofluid, Superhydrophobic surface, Wetting transition}, pubstate = {published}, tppubtype = {article} } We investigated manipulating wetting transitions of ferrofluid droplets on planar superhydrophobic surfaces by electromagnetic stimulation. We showed that even if magnetic forces are small at small liquid volumes (1–10 μl), they can be effectively used to induce Cassie to Wenzel transition when the exciting frequency is close to the resonant frequency. We related the wetting transition to the increase of the Laplace pressure as a consequence of the large deformation that occurs close to the resonant frequency; on the contrary, inertia forces were not able to induce such a transition. This study promises a new approach to manipulate ferrofluid droplets for various microfluidic and lab-on-chip technologies. | |

73. | Issa, Khaled; Poesio, Pietro Algorithm to enforce uniform density in liquid atomistic subdomains with specular boundaries Journal Article Physical Review E, 89 (4), pp. 043307, 2014. Abstract | BibTeX | Tags: Atomistic, Specular Boundaries | Links: @article{Issa2014, title = {Algorithm to enforce uniform density in liquid atomistic subdomains with specular boundaries}, author = {Khaled M. Issa and Pietro Poesio}, doi = {http://dx.doi.org/10.1103/PhysRevE.89.043307}, year = {2014}, date = {2014-04-15}, journal = {Physical Review E}, volume = {89}, number = {4}, pages = {043307}, abstract = {An important component in hybrid atomistic-continuum (HAC) modeling of liquids is the proper termination of the atomistic subdomain (ΩA). When the HAC model is based on the Schwarz domain decomposition method, the total number of particles in ΩA is conserved using specular boundaries in an overlap region, where information is exchanged with the continuum subdomain (ΩC). This non-periodic termination of ΩA fails to account for forces otherwise included in a periodic system, through the minimum image convention. The absence of such forces results in spurious density fluctuations adjacent to the specular boundaries. In this work, we present a new boundary force algorithm that establishes a uniform density profile at non-periodic boundaries of ΩA. We also examine the effects of the non-periodic termination of ΩA on the liquid properties. The algorithm relies on force measurements carried out over a spatially discretized atomistic subdomain. It is relatively straightforward to implement and can be seamlessly extended to higher dimensions.}, keywords = {Atomistic, Specular Boundaries}, pubstate = {published}, tppubtype = {article} } An important component in hybrid atomistic-continuum (HAC) modeling of liquids is the proper termination of the atomistic subdomain (ΩA). When the HAC model is based on the Schwarz domain decomposition method, the total number of particles in ΩA is conserved using specular boundaries in an overlap region, where information is exchanged with the continuum subdomain (ΩC). This non-periodic termination of ΩA fails to account for forces otherwise included in a periodic system, through the minimum image convention. The absence of such forces results in spurious density fluctuations adjacent to the specular boundaries. In this work, we present a new boundary force algorithm that establishes a uniform density profile at non-periodic boundaries of ΩA. We also examine the effects of the non-periodic termination of ΩA on the liquid properties. The algorithm relies on force measurements carried out over a spatially discretized atomistic subdomain. It is relatively straightforward to implement and can be seamlessly extended to higher dimensions. | |

72. | Picchi, Davide; Correra, Sebastiano; Poesio, Pietro Flow pattern transition, pressure gradient, hold-up predictions in gas/non-Newtonian power-law fluid stratified flow Journal Article International Journal of Multiphase Flow, 63 , pp. 105-115, 2014. Abstract | BibTeX | Tags: Flow pattern maps, Hold-up, Non-Newtonian power-law fluid, Pressure gradient, Stratified flow, Two-fluid model | Links: @article{Picchi2014-2, title = {Flow pattern transition, pressure gradient, hold-up predictions in gas/non-Newtonian power-law fluid stratified flow}, author = {Davide Picchi and Sebastiano Correra and Pietro Poesio}, doi = {10.1016/j.ijmultiphaseflow.2014.03.005}, year = {2014}, date = {2014-04-05}, journal = {International Journal of Multiphase Flow}, volume = {63}, pages = {105-115}, abstract = {This work focuses on gas/non-Newtonian power-law fluid stratified pipe flow. Two different theoretical approaches to obtain pressure gradient and hold-up predictions are presented: the steady fully developed two-fluid model and the pre-integrated model. The theoretical predictions are compared with experimental data available for horizontal and for slightly downward inclined air/shear thinning fluid stratified flow taken from literature. The predictions of the pre-integrated model are validated showing a good agreement when compared with experimental data. The criteria for the transition from the stratified flow pattern are applied to gas/non-Newtonian stratified flow. The neutral stability analysis (smooth/wavy stratified flow) and the well-posedness (existence region of stratified flow) of governing equations are carry out. The predicted transition boundaries are obtained using the steady fully developed two-fluid model and the pre-integrated model, where the shape factors and their derivatives are accounted for. A comparison between the predicted boundaries and experimental flow pattern maps is presented and shows a good agreement. A comment on the shear stress modeling by the pre-integrated model is provided.}, keywords = {Flow pattern maps, Hold-up, Non-Newtonian power-law fluid, Pressure gradient, Stratified flow, Two-fluid model}, pubstate = {published}, tppubtype = {article} } This work focuses on gas/non-Newtonian power-law fluid stratified pipe flow. Two different theoretical approaches to obtain pressure gradient and hold-up predictions are presented: the steady fully developed two-fluid model and the pre-integrated model. The theoretical predictions are compared with experimental data available for horizontal and for slightly downward inclined air/shear thinning fluid stratified flow taken from literature. The predictions of the pre-integrated model are validated showing a good agreement when compared with experimental data. The criteria for the transition from the stratified flow pattern are applied to gas/non-Newtonian stratified flow. The neutral stability analysis (smooth/wavy stratified flow) and the well-posedness (existence region of stratified flow) of governing equations are carry out. The predicted transition boundaries are obtained using the steady fully developed two-fluid model and the pre-integrated model, where the shape factors and their derivatives are accounted for. A comparison between the predicted boundaries and experimental flow pattern maps is presented and shows a good agreement. A comment on the shear stress modeling by the pre-integrated model is provided. | |

71. | Ooms, Gijs; Poesio, Pietro Analytical study of slightly eccentric core–annular flow Journal Article Journal of Engineering Mathematics, 85 (1), pp. 65-81, 2014. Abstract | BibTeX | Tags: Core–annular flow pattern, Theoretical model, Two-phase flow | Links: @article{Ooms_Poesio_2014, title = {Analytical study of slightly eccentric core–annular flow}, author = {Gijs Ooms and Pietro Poesio}, doi = {10.1007/s10665-013-9630-0}, year = {2014}, date = {2014-04-01}, journal = {Journal of Engineering Mathematics}, volume = {85}, number = {1}, pages = {65-81}, abstract = {An analytical study was conducted on the flow of a rigid core surrounded by an annular liquid layer through a horizontal tube. Special emphasis was placed on the question how the buoyancy force on the core, caused by a possible density difference between the core and the annular layer, is counterbalanced. The analysis was carried out under the following restrictions: Stokes flow (no inertia), gap between the core and tube wall small compared with the tube radius, and eccentricity small compared with the gap between the core and the tube wall. A perturbation calculation was carried out with the amplitude of the wave at the core–annular interface as small parameter. The restoring (levitation) force is due to the viscous force exerted by the azimuthal velocity components on the core.}, keywords = {Core–annular flow pattern, Theoretical model, Two-phase flow}, pubstate = {published}, tppubtype = {article} } An analytical study was conducted on the flow of a rigid core surrounded by an annular liquid layer through a horizontal tube. Special emphasis was placed on the question how the buoyancy force on the core, caused by a possible density difference between the core and the annular layer, is counterbalanced. The analysis was carried out under the following restrictions: Stokes flow (no inertia), gap between the core and tube wall small compared with the tube radius, and eccentricity small compared with the gap between the core and the tube wall. A perturbation calculation was carried out with the amplitude of the wave at the core–annular interface as small parameter. The restoring (levitation) force is due to the viscous force exerted by the azimuthal velocity components on the core. | |

70. | Farsetti, Silvia; Farisè, Stefano; Poesio, Pietro Experimental investigation of high viscosity oil–air intermittent flow Journal Article Experimental Thermal and Fluid Science, 57 , pp. 285-292, 2014. Abstract | BibTeX | Tags: Air–oil flow, Frequency, Highly viscous oil, Hold-up, Slug flow | Links: @article{Farsetti2014, title = {Experimental investigation of high viscosity oil–air intermittent flow}, author = {Silvia Farsetti and Stefano Farisè and Pietro Poesio}, doi = {10.1016/j.expthermflusci.2013.12.004}, year = {2014}, date = {2014-03-27}, journal = {Experimental Thermal and Fluid Science}, volume = {57}, pages = {285-292}, abstract = {In this work, we investigated experimentally the flow of high viscosity-oil (0.9 Pa s) and gas in a horizontal and inclined pipe providing new data-sets on high-viscosity oil multiphase pipe flows that include experimental pressure drops, bubble frequencies and lengths, holdups measured using capacitance probes. All the experimental results are compared to models or correlations present in the literature and widely used, and validated, for low-viscosity liquids multiphase flows. The main conclusion is that correlation available in literature (validated and extensively tested for the low viscosity liquid case) cannot be extended to the high viscosity case.}, keywords = {Air–oil flow, Frequency, Highly viscous oil, Hold-up, Slug flow}, pubstate = {published}, tppubtype = {article} } In this work, we investigated experimentally the flow of high viscosity-oil (0.9 Pa s) and gas in a horizontal and inclined pipe providing new data-sets on high-viscosity oil multiphase pipe flows that include experimental pressure drops, bubble frequencies and lengths, holdups measured using capacitance probes. All the experimental results are compared to models or correlations present in the literature and widely used, and validated, for low-viscosity liquids multiphase flows. The main conclusion is that correlation available in literature (validated and extensively tested for the low viscosity liquid case) cannot be extended to the high viscosity case. | |

69. | Zanchini, Enzo; Beretta, Gian Paolo Recent Progress in the Definition of Thermodynamic Entropy Journal Article Entropy, 16 (3), pp. 1547-1570, 2014. Abstract | BibTeX | Tags: entropy, non-simple systems, nonequilibrium states, operational definition | Links: @article{Zanchini_Beretta_2014, title = {Recent Progress in the Definition of Thermodynamic Entropy}, author = {Enzo Zanchini and Gian Paolo Beretta}, doi = {10.3390/e16031547}, year = {2014}, date = {2014-03-19}, journal = {Entropy}, volume = {16}, number = {3}, pages = {1547-1570}, abstract = {The principal methods for the definition of thermodynamic entropy are discussed with special reference to those developed by Carathéodory, the Keenan School, Lieb and Yngvason, and the present authors. An improvement of the latter method is then presented. Seven basic axioms are employed: three Postulates, which are considered as having a quite general validity, and four Assumptions, which identify the domains of validity of the definitions of energy (Assumption 1) and entropy (Assumptions 2, 3, 4). The domain of validity of the present definition of entropy is not restricted to stable equilibrium states. For collections of simple systems, it coincides with that of the proof of existence and uniqueness of an entropy function which characterizes the relation of adiabatic accessibility proposed by Lieb and Yngvason. However, our treatment does not require the formation of scaled copies so that it applies not only to collections of simple systems, but also to systems contained in electric or magnetic fields and to small and few-particle systems.}, keywords = {entropy, non-simple systems, nonequilibrium states, operational definition}, pubstate = {published}, tppubtype = {article} } The principal methods for the definition of thermodynamic entropy are discussed with special reference to those developed by Carathéodory, the Keenan School, Lieb and Yngvason, and the present authors. An improvement of the latter method is then presented. Seven basic axioms are employed: three Postulates, which are considered as having a quite general validity, and four Assumptions, which identify the domains of validity of the definitions of energy (Assumption 1) and entropy (Assumptions 2, 3, 4). The domain of validity of the present definition of entropy is not restricted to stable equilibrium states. For collections of simple systems, it coincides with that of the proof of existence and uniqueness of an entropy function which characterizes the relation of adiabatic accessibility proposed by Lieb and Yngvason. However, our treatment does not require the formation of scaled copies so that it applies not only to collections of simple systems, but also to systems contained in electric or magnetic fields and to small and few-particle systems. | |

68. | Demori, Marco; Ferrari, Vittorio; Farisè, Stefano; Poesio, Pietro Piezoelectric energy harvesting from von Karman vortices Incollection Sensors and Microsystems, 268 , pp. 417-421, 2014. Abstract | BibTeX | Tags: Piezoeletric energy harvesting, Von Karman vortices | Links: @incollection{Demori_Ferrari_Conf_2014, title = {Piezoelectric energy harvesting from von Karman vortices}, author = {Marco Demori and Vittorio Ferrari and Stefano Farisè and Pietro Poesio}, doi = {10.1007/978-3-319-00684-0_80}, year = {2014}, date = {2014-01-01}, booktitle = {Sensors and Microsystems}, journal = {Sensors and Microsystems - Lecture Notes in Electrical Engineering}, volume = {268}, pages = {417-421}, series = {Lecture Notes in Electrical Engineering}, abstract = {In this paper a study of an innovative energy-harvesting system based on a piezoelectric converter to recover energy from an airflow is presented. The converter is embedded as a part of an oscillating beam, and it is used to harvest energy from the vibrations induced by von Karman vortices detached from a bluff body placed upstream. The system has been placed in a wind tunnel in order to measure the converter voltage and the harvested power for different flow velocities and beam orientations with respect to the flow direction. Experimental results confirm the von Karman vortices as the forcing for the beam oscillations. The possibility to optimize the harvesting effectiveness with the proper beam orientation and flow velocity has been demonstrated.}, keywords = {Piezoeletric energy harvesting, Von Karman vortices}, pubstate = {published}, tppubtype = {incollection} } In this paper a study of an innovative energy-harvesting system based on a piezoelectric converter to recover energy from an airflow is presented. The converter is embedded as a part of an oscillating beam, and it is used to harvest energy from the vibrations induced by von Karman vortices detached from a bluff body placed upstream. The system has been placed in a wind tunnel in order to measure the converter voltage and the harvested power for different flow velocities and beam orientations with respect to the flow direction. Experimental results confirm the von Karman vortices as the forcing for the beam oscillations. The possibility to optimize the harvesting effectiveness with the proper beam orientation and flow velocity has been demonstrated. | |

## 2013 |
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67. | Sun, Chengzhen; Boutilier, Michael; Au, Harold; Poesio, Pietro; Bai, Bofeng; Karnik, Rohit; Hadjiconstantinou, Nicolas Mechanisms of Molecular Permeation through Nanoporous Graphene Membranes Journal Article Langmuir, 30 (2), pp. 675-682, 2013. Abstract | BibTeX | Tags: Graphene, Molecular permeation, Nanoporous membranes | Links: @article{Sun_Poesio_2013, title = {Mechanisms of Molecular Permeation through Nanoporous Graphene Membranes}, author = {Chengzhen Sun and Michael S. H. Boutilier and Harold Au and Pietro Poesio and Bofeng Bai and Rohit Karnik and Nicolas G. Hadjiconstantinou}, doi = {10.1021/la403969g}, year = {2013}, date = {2013-12-23}, journal = {Langmuir}, volume = {30}, number = {2}, pages = {675-682}, abstract = {We present an investigation of molecular permeation of gases through nanoporous graphene membranes via molecular dynamics simulations; four different gases are investigated, namely helium, hydrogen, nitrogen, and methane. We show that in addition to the direct (gas-kinetic) flux of molecules crossing from the bulk phase on one side of the graphene to the bulk phase on the other side, for gases that adsorb onto the graphene, significant contribution to the flux across the membrane comes from a surface mechanism by which molecules cross after being adsorbed onto the graphene surface. Our results quantify the relative contribution of the bulk and surface mechanisms and show that the direct flux can be described reasonably accurately using kinetic theory, provided the latter is appropriately modified assuming steric molecule–pore interactions, with gas molecules behaving as hard spheres of known kinetic diameters. The surface flux is negligible for gases that do not adsorb onto graphene (e.g., He and H2), while for gases that adsorb (e.g., CH4 and N2) it can be on the order of the direct flux or larger. Our results identify a nanopore geometry that is permeable to hydrogen and helium, is significantly less permeable to nitrogen, and is essentially impermeable to methane, thus validating previous suggestions that nanoporous graphene membranes can be used for gas separation. We also show that molecular permeation is strongly affected by pore functionalization; this observation may be sufficient to explain the large discrepancy between simulated and experimentally measured transport rates through nanoporous graphene membranes.}, keywords = {Graphene, Molecular permeation, Nanoporous membranes}, pubstate = {published}, tppubtype = {article} } We present an investigation of molecular permeation of gases through nanoporous graphene membranes via molecular dynamics simulations; four different gases are investigated, namely helium, hydrogen, nitrogen, and methane. We show that in addition to the direct (gas-kinetic) flux of molecules crossing from the bulk phase on one side of the graphene to the bulk phase on the other side, for gases that adsorb onto the graphene, significant contribution to the flux across the membrane comes from a surface mechanism by which molecules cross after being adsorbed onto the graphene surface. Our results quantify the relative contribution of the bulk and surface mechanisms and show that the direct flux can be described reasonably accurately using kinetic theory, provided the latter is appropriately modified assuming steric molecule–pore interactions, with gas molecules behaving as hard spheres of known kinetic diameters. The surface flux is negligible for gases that do not adsorb onto graphene (e.g., He and H2), while for gases that adsorb (e.g., CH4 and N2) it can be on the order of the direct flux or larger. Our results identify a nanopore geometry that is permeable to hydrogen and helium, is significantly less permeable to nitrogen, and is essentially impermeable to methane, thus validating previous suggestions that nanoporous graphene membranes can be used for gas separation. We also show that molecular permeation is strongly affected by pore functionalization; this observation may be sufficient to explain the large discrepancy between simulated and experimentally measured transport rates through nanoporous graphene membranes. | |

66. | Beretta, Gian Paolo; Iora, Paolo; Ghoniem, Ahmed Allocating electricity production from a hybrid fossil-renewable power plant among its multi primary resources Journal Article Energy, 60 , pp. 344-360, 2013. Abstract | BibTeX | Tags: allocation methods in cogeneration and hybrid facilities, hybrid power production, primary energy factors, solar-integrated power plants | Links: @article{Beretta_Iora_2013, title = {Allocating electricity production from a hybrid fossil-renewable power plant among its multi primary resources}, author = {Gian Paolo Beretta and Paolo Iora and Ahmed F. Ghoniem}, doi = {10.1016/j.energy.2013.07.047}, year = {2013}, date = {2013-10-01}, journal = {Energy}, volume = {60}, pages = {344-360}, abstract = {The interest in hybrid power production facilities, based on the integration of renewable resources and conventional fossil fuels, is rapidly rising. The question of what fraction of the electricity produced in such facilities is to be considered as produced from the renewable resources is still being debated. We show that the conventional Fossil-Centered-Solar-Share method and the Exergy-based method lead to unfair allocations that may result in unfair access to subsidies granted to renewable electricity. We propose a more balanced Single-Resource-Separate-Production-Reference (SRSPR) allocation method based on prescribed reference partial primary energy factors chosen by some authority to represent reference efficiencies of non-hybrid power production from the same renewable and fossil resources used by the hybrid facility. We then show that as hybridization gains higher fractions of the local energy market, the SRSPR method may still result in somewhat unfair allocations leading to local market distortions. To overcome this drawback, we formulate a more consistent Self-Tuned-Average-Local-Productions-Reference (STALPR) allocation method whereby the electricity allocation fractions are based on the average partial primary energy factors of the actual energy portfolio of the local area that includes the hybrid plant itself. Results are illustrated with reference to a solar-integrated combined cycle facility.}, keywords = {allocation methods in cogeneration and hybrid facilities, hybrid power production, primary energy factors, solar-integrated power plants}, pubstate = {published}, tppubtype = {article} } The interest in hybrid power production facilities, based on the integration of renewable resources and conventional fossil fuels, is rapidly rising. The question of what fraction of the electricity produced in such facilities is to be considered as produced from the renewable resources is still being debated. We show that the conventional Fossil-Centered-Solar-Share method and the Exergy-based method lead to unfair allocations that may result in unfair access to subsidies granted to renewable electricity. We propose a more balanced Single-Resource-Separate-Production-Reference (SRSPR) allocation method based on prescribed reference partial primary energy factors chosen by some authority to represent reference efficiencies of non-hybrid power production from the same renewable and fossil resources used by the hybrid facility. We then show that as hybridization gains higher fractions of the local energy market, the SRSPR method may still result in somewhat unfair allocations leading to local market distortions. To overcome this drawback, we formulate a more consistent Self-Tuned-Average-Local-Productions-Reference (STALPR) allocation method whereby the electricity allocation fractions are based on the average partial primary energy factors of the actual energy portfolio of the local area that includes the hybrid plant itself. Results are illustrated with reference to a solar-integrated combined cycle facility. | |

## 2012 |
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65. | Poesio, Pietro; Strazza, Domenico; Sotgia, Giorgio Two- and three-phase mixtures of highly-viscous-oil/water/air in a 50 mm i.d. pipe Journal Article Applied Thermal Engineering, 49 , pp. 41-47, 2012. Abstract | BibTeX | Tags: Core-annular, Heavy oils, Three-phase flows | Links: @article{Poesio_Strazza_Sotgia_2012, title = {Two- and three-phase mixtures of highly-viscous-oil/water/air in a 50 mm i.d. pipe}, author = {Pietro Poesio and Domenico Strazza and Giorgio Sotgia}, doi = {10.1016/j.applthermaleng.2011.04.052}, year = {2012}, date = {2012-12-31}, journal = {Applied Thermal Engineering}, volume = {49}, pages = {41-47}, abstract = {A three-phase flow of oil, water and gas through a pipeline often occurs in industry. It is important to study such flows in order to be able to design a three-phase flow pipeline. To that purpose experiments with oil, water and air in a 50 mm i.d. plastic pipe have been carried out to derive a new data set for a three-phase flow in horizontal configuration. First, we investigate the pressure drop showing the influence of air injection on the two-phase flow reference flow pattern. Then we underline the strong link between the qualitative behavior of the three-phase pressure drop reduction factor and the two-phase flow reference flow pattern.}, keywords = {Core-annular, Heavy oils, Three-phase flows}, pubstate = {published}, tppubtype = {article} } A three-phase flow of oil, water and gas through a pipeline often occurs in industry. It is important to study such flows in order to be able to design a three-phase flow pipeline. To that purpose experiments with oil, water and air in a 50 mm i.d. plastic pipe have been carried out to derive a new data set for a three-phase flow in horizontal configuration. First, we investigate the pressure drop showing the influence of air injection on the two-phase flow reference flow pattern. Then we underline the strong link between the qualitative behavior of the three-phase pressure drop reduction factor and the two-phase flow reference flow pattern. | |

64. | Demori, Marco; Ferrari, Vittorio; Farisè, Stefano; Poesio, Pietro; Pedrazzani, Roberta; Steimberg,; Boniotti,; Mazzoleni, Microfluidic sensor for noncontact detection of cell flow in a microchannel Journal Article Procedia Engineering - EUROSENSORS 2012, the 26th European Conference on Solid-State Transducers, 47 , pp. 1247-1250, 2012. Abstract | BibTeX | Tags: cell counting, cell flow detection, impedance sensing, microfluidic sensor | Links: @article{Demori_Ferrari_Conf_2012, title = {Microfluidic sensor for noncontact detection of cell flow in a microchannel}, author = {Marco Demori and Vittorio Ferrari and Stefano Farisè and Pietro Poesio and Roberta Pedrazzani and N. Steimberg and J. Boniotti and G. Mazzoleni}, doi = {10.1016/j.proeng.2012.09.379}, year = {2012}, date = {2012-12-01}, journal = {Procedia Engineering - EUROSENSORS 2012, the 26th European Conference on Solid-State Transducers}, volume = {47}, pages = {1247-1250}, abstract = {A microfluidic sensor for detection of cells flowing in a microchannel is presented. The sensor consists of a PDMS (PolyDiMethylSiloxane) layer with two planar microreservoirs connected by a microchannel. The bottom sides of the microreservoirs are faced to two sensing electrodes realized on a PCB (Printed Circuit Board). A noncontact measurement is ensured by an insulator layer between the electrodes and the fluid. Particles flowing in the microchannel cause changes in the conductivity of the narrow path formed by the fluid, producing variations in the impedance between the electrodes. A tailored electronic interface based on a DDS (Direct Digital Synthesis) device is proposed to measure the impedance variations. In the experimental tests, the cell flow is detected by changes in the effective capacitance and conductance between electrodes. These preliminary results are promising for biological measurements such as counting and sizing of cells in different matrices.}, keywords = {cell counting, cell flow detection, impedance sensing, microfluidic sensor}, pubstate = {published}, tppubtype = {article} } A microfluidic sensor for detection of cells flowing in a microchannel is presented. The sensor consists of a PDMS (PolyDiMethylSiloxane) layer with two planar microreservoirs connected by a microchannel. The bottom sides of the microreservoirs are faced to two sensing electrodes realized on a PCB (Printed Circuit Board). A noncontact measurement is ensured by an insulator layer between the electrodes and the fluid. Particles flowing in the microchannel cause changes in the conductivity of the narrow path formed by the fluid, producing variations in the impedance between the electrodes. A tailored electronic interface based on a DDS (Direct Digital Synthesis) device is proposed to measure the impedance variations. In the experimental tests, the cell flow is detected by changes in the effective capacitance and conductance between electrodes. These preliminary results are promising for biological measurements such as counting and sizing of cells in different matrices. | |

63. | Strazza, Domenico; Poesio, Pietro Experimental study on the restart of core-annular flow Journal Article Chemical Engineering Research and Design, 90 (11), pp. 1711-1718, 2012. Abstract | BibTeX | Tags: Core-annular flow Restart, Oil–water, Pressure drops | Links: @article{Strazza_Poesio_2012, title = {Experimental study on the restart of core-annular flow}, author = {Domenico Strazza and Pietro Poesio}, doi = {10.1016/j.cherd.2012.03.011}, year = {2012}, date = {2012-11-01}, journal = {Chemical Engineering Research and Design}, volume = {90}, number = {11}, pages = {1711-1718}, abstract = {We show the results of an experimental campaign to study the pressure drop during the restart of a core-annular flow from a stratified configuration. In normal core annular flow operations, due to fouling or pump failures, a core flow may not be sustained anymore and hence it stratifies. Since the pressure drops connected to the stratified flow regime are much larger than the ones of core annular, the flow suddenly stops. To restart it there are two possibilities: one is to try to provide a higher pressure gradient trying to restore the flow of water and oil, the other is to clean the pipe using water only: in both cases an attachment of a thin layer of oil on the pipe internal wall occurs and the pressure drop for water only or oil–water are higher than the previous ones with clean pipe wall. We focused our attention on the cleaning by water only and we provide experimental data on the evolution of the pressure drop as function of time in order to find when the pipe could be considered as perfectly cleaned or, at least, when the pressure drop are low enough to restart the oil flow. The experimental results are finally compared with a two-fluid model available in literature.}, keywords = {Core-annular flow Restart, Oil–water, Pressure drops}, pubstate = {published}, tppubtype = {article} } We show the results of an experimental campaign to study the pressure drop during the restart of a core-annular flow from a stratified configuration. In normal core annular flow operations, due to fouling or pump failures, a core flow may not be sustained anymore and hence it stratifies. Since the pressure drops connected to the stratified flow regime are much larger than the ones of core annular, the flow suddenly stops. To restart it there are two possibilities: one is to try to provide a higher pressure gradient trying to restore the flow of water and oil, the other is to clean the pipe using water only: in both cases an attachment of a thin layer of oil on the pipe internal wall occurs and the pressure drop for water only or oil–water are higher than the previous ones with clean pipe wall. We focused our attention on the cleaning by water only and we provide experimental data on the evolution of the pressure drop as function of time in order to find when the pipe could be considered as perfectly cleaned or, at least, when the pressure drop are low enough to restart the oil flow. The experimental results are finally compared with a two-fluid model available in literature. | |

62. | Farisè, Stefano; Franzoni, Andrea; Poesio, Pietro; Beretta, Gian Paolo Heat transfer enhancement by spinodal decomposition in micro heat exchangers Journal Article Experimental Thermal and Fluid Science, 42 (2012), pp. 38-45, 2012. Abstract | BibTeX | Tags: Microcooling, Microdevice, Spinodal decomposition | Links: @article{Farisè_Franzoni_Poesio_2012, title = {Heat transfer enhancement by spinodal decomposition in micro heat exchangers}, author = {Stefano Farisè and Andrea Franzoni and Pietro Poesio and Gian Paolo Beretta}, doi = {10.1016/j.expthermflusci.2012.03.024}, year = {2012}, date = {2012-10-01}, journal = {Experimental Thermal and Fluid Science}, volume = {42}, number = {2012}, pages = {38-45}, abstract = {In this work, we investigate experimentally how the heat transfer in a laminar flow can be enhanced by using a partially miscible binary liquid–liquid mixture undergoing spinodal decomposition. A mixture of acetone–hexadecane is quenched in a micro heat exchanger to induce spinodal decomposition. The heat transfer rate is enhanced by self-induced convective effects sustained by the free energy liberated during phase separation. We report a heat-transfer augmentation of up to 150% when phase separation occurs in microchannels. Since acetone and hexadecane are immiscible below a critical temperature of 27 °C, to obtain their spinodal decomposition the mixture inlet temperature are above 27 °C and the heat exchangers wall are well below. We measure the heat transfer with a feedback method instead of a direct measure. To validate this measuring technique we carefully verify the energy balance. We fabricated a copper single-channel heat sink and two different types of multi-channel array. The single-channel exchanger allows us to visualize the induced convection. The arrays of microchannels promise to achieve very high heat transfer coefficients with small flow rate.}, keywords = {Microcooling, Microdevice, Spinodal decomposition}, pubstate = {published}, tppubtype = {article} } In this work, we investigate experimentally how the heat transfer in a laminar flow can be enhanced by using a partially miscible binary liquid–liquid mixture undergoing spinodal decomposition. A mixture of acetone–hexadecane is quenched in a micro heat exchanger to induce spinodal decomposition. The heat transfer rate is enhanced by self-induced convective effects sustained by the free energy liberated during phase separation. We report a heat-transfer augmentation of up to 150% when phase separation occurs in microchannels. Since acetone and hexadecane are immiscible below a critical temperature of 27 °C, to obtain their spinodal decomposition the mixture inlet temperature are above 27 °C and the heat exchangers wall are well below. We measure the heat transfer with a feedback method instead of a direct measure. To validate this measuring technique we carefully verify the energy balance. We fabricated a copper single-channel heat sink and two different types of multi-channel array. The single-channel exchanger allows us to visualize the induced convection. The arrays of microchannels promise to achieve very high heat transfer coefficients with small flow rate. | |

61. | Beretta, Gian Paolo; Iora, Paolo; Ghoniem, Ahmed Novel approach for fair allocation of primary energy consumption among cogenerated energy-intensive products based on the actual local area production scenario Journal Article Energy, 44 (1), pp. 1107-1120, 2012. Abstract | BibTeX | Tags: Allocation methods in cogeneration, Cogeneration regulation, Multi-generation, primary energy factors | Links: @article{Beretta_Iora_2012, title = {Novel approach for fair allocation of primary energy consumption among cogenerated energy-intensive products based on the actual local area production scenario}, author = {Gian Paolo Beretta and Paolo Iora and Ahmed F. Ghoniem}, doi = {10.1016/j.energy.2012.04.047}, year = {2012}, date = {2012-08-01}, journal = {Energy}, volume = {44}, number = {1}, pages = {1107-1120}, abstract = {Multi-generation facilities are almost always part of a local production scenario, i.e., a local area (district, city, regional, national, interstate) energy system providing end users with electricity, residential heating or air-conditioning, industrial process steam, desalinated water, and/or other energy-intensive products. Because of the growth of energy consumption and environmental concerns, local, national, and international regulations and standards tend to incorporate and enforce methods for energy and environmental rating of the end uses of primary energy. Important to such methods, is the definition of fair criteria to allocate fuel consumption among cogenerated products. Allocation based on prescribed primary energy factors for each product corresponding to the average efficiencies of separate production facilities may result in unfair figures and inconsistencies which become increasingly important as cogeneration gains higher fractions of the local energy market. To overcome this problem, we propose a slightly more elaborate, but self-consistent method whereby the allocation is adaptive and self-tuned to the local energy scenario. For heat and power cogeneration, we propose to allocate fuel consumption on the basis of the average primary energy factors for electricity and heat in the given local area including the cogeneration facility of interest. We call it the Self-Tuned Average-Local-Productions Reference (STALPR) method.}, keywords = {Allocation methods in cogeneration, Cogeneration regulation, Multi-generation, primary energy factors}, pubstate = {published}, tppubtype = {article} } Multi-generation facilities are almost always part of a local production scenario, i.e., a local area (district, city, regional, national, interstate) energy system providing end users with electricity, residential heating or air-conditioning, industrial process steam, desalinated water, and/or other energy-intensive products. Because of the growth of energy consumption and environmental concerns, local, national, and international regulations and standards tend to incorporate and enforce methods for energy and environmental rating of the end uses of primary energy. Important to such methods, is the definition of fair criteria to allocate fuel consumption among cogenerated products. Allocation based on prescribed primary energy factors for each product corresponding to the average efficiencies of separate production facilities may result in unfair figures and inconsistencies which become increasingly important as cogeneration gains higher fractions of the local energy market. To overcome this problem, we propose a slightly more elaborate, but self-consistent method whereby the allocation is adaptive and self-tuned to the local energy scenario. For heat and power cogeneration, we propose to allocate fuel consumption on the basis of the average primary energy factors for electricity and heat in the given local area including the cogeneration facility of interest. We call it the Self-Tuned Average-Local-Productions Reference (STALPR) method. | |

60. | Beretta, Gian Paolo Quantum thermodynamic Carnot and Otto-like cycles for a two-level system Journal Article Europhysics Letters, 99 (2), pp. 200005, 2012. Abstract | BibTeX | Tags: Carnot cycle, Otto-like cycles, quantum thermodinamics, two-level system | Links: @article{Beretta_2012, title = {Quantum thermodynamic Carnot and Otto-like cycles for a two-level system}, author = {Gian Paolo Beretta}, doi = {10.1209/0295-5075/99/20005}, year = {2012}, date = {2012-07-18}, journal = {Europhysics Letters}, volume = {99}, number = {2}, pages = {200005}, abstract = {Within the recent revival of interest in quantum heat engines between two thermal reservoirs whereby the working substance is a two-level system, it has been suggested that the celebrated Carnot heat-to-work conversion efficiency 1 − (Tlow/Thigh) cannot be reached. Contrary to this suggestion, we show that reaching the Carnot bound not only is not impossible and does not require an infinite number of heat baths and infinitesimal processes, but it is also within reach of the current experimental techniques. It is sufficient to cycle smoothly (slowly) over at least three (in general four) values of the tunable energy level gap Δ of the system, by varying Δ not only along the isoentropics, but also along the isotherms. This is possible by means of the recently suggested maser-laser tandem technique. We base our proof on the general thermodynamic equilibrium properties of a two-level system together with a careful distinction between the Gibbs relation dE = T dS + (E/Δ) dΔ and the energy balance equation ${mathrm { d}}E=delta Q^leftarrow - delta W^rightarrow $ . We derive bounds to the net-work to high-temperature-heat ratio (energy efficiency) for a Carnot cycle and for the "inscribed" Otto-like cycle. By representing these cycles on useful thermodynamic diagrams, we infer and confirm important aspects of the second law of thermodynamics.}, keywords = {Carnot cycle, Otto-like cycles, quantum thermodinamics, two-level system}, pubstate = {published}, tppubtype = {article} } Within the recent revival of interest in quantum heat engines between two thermal reservoirs whereby the working substance is a two-level system, it has been suggested that the celebrated Carnot heat-to-work conversion efficiency 1 − (Tlow/Thigh) cannot be reached. Contrary to this suggestion, we show that reaching the Carnot bound not only is not impossible and does not require an infinite number of heat baths and infinitesimal processes, but it is also within reach of the current experimental techniques. It is sufficient to cycle smoothly (slowly) over at least three (in general four) values of the tunable energy level gap Δ of the system, by varying Δ not only along the isoentropics, but also along the isotherms. This is possible by means of the recently suggested maser-laser tandem technique. We base our proof on the general thermodynamic equilibrium properties of a two-level system together with a careful distinction between the Gibbs relation dE = T dS + (E/Δ) dΔ and the energy balance equation ${mathrm { d}}E=delta Q^leftarrow - delta W^rightarrow $ . We derive bounds to the net-work to high-temperature-heat ratio (energy efficiency) for a Carnot cycle and for the "inscribed" Otto-like cycle. By representing these cycles on useful thermodynamic diagrams, we infer and confirm important aspects of the second law of thermodynamics. | |

59. | Ooms, Gijs; Pourquie, Mathieu; Poesio, Pietro Numerical study of eccentric core-annular flow Journal Article International Journal of Multiphase Flow, 42 , pp. 74-79, 2012. Abstract | BibTeX | Tags: Core-annular flow pattern, Numerical calculation, Two-phase flow | Links: @article{Ooms_Pourquie_Poesio_2012, title = {Numerical study of eccentric core-annular flow}, author = {Gijs Ooms and Mathieu J. B. M. Pourquie and Pietro Poesio}, doi = {10.1016/j.ijmultiphaseflow.2012.01.012}, year = {2012}, date = {2012-06-01}, journal = {International Journal of Multiphase Flow}, volume = {42}, pages = {74-79}, abstract = {A numerical study (taking into account inertial -, viscous - and pressure forces) has been made of eccentric core-annular flow through a horizontal pipe, special attention being paid to the vertical force on the core. The viscosity of the core is assumed to be so large that it behaves as a rigid solid. A wave is present at its surface. The shape of the wave is based on experimental results published earlier in the open literature. Due to the eccentricity the centre line of the core is shifted in the upward vertical direction with respect to the centre line of the tube. The vertical force on the core was found to be dependent on the Reynolds number: at small values of the Reynolds number the force is in the upward vertical direction, at large values the force is downward. This means that at large values of the Reynolds number an upward buoyancy force on the core due to a density difference between core and annulus can be counterbalanced. So a stationary core-annular flow is then possible.}, keywords = {Core-annular flow pattern, Numerical calculation, Two-phase flow}, pubstate = {published}, tppubtype = {article} } A numerical study (taking into account inertial -, viscous - and pressure forces) has been made of eccentric core-annular flow through a horizontal pipe, special attention being paid to the vertical force on the core. The viscosity of the core is assumed to be so large that it behaves as a rigid solid. A wave is present at its surface. The shape of the wave is based on experimental results published earlier in the open literature. Due to the eccentricity the centre line of the core is shifted in the upward vertical direction with respect to the centre line of the tube. The vertical force on the core was found to be dependent on the Reynolds number: at small values of the Reynolds number the force is in the upward vertical direction, at large values the force is downward. This means that at large values of the Reynolds number an upward buoyancy force on the core due to a density difference between core and annulus can be counterbalanced. So a stationary core-annular flow is then possible. | |

58. | DiFede, Fabio; Poesio, Pietro; Beretta, Gian Paolo Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity, liquid–liquid, strongly non-regular mixture Journal Article International Journal of Heat and Mass Transfer, 55 (4), pp. 897-906, 2012. Abstract | BibTeX | Tags: Heat transfer enhancement, Spinodal decomposition | Links: @article{DiFede_Poesio_Beretta_2012, title = {Heat transfer enhancement in a small pipe by spinodal decomposition of a low viscosity, liquid–liquid, strongly non-regular mixture}, author = {Fabio DiFede and Pietro Poesio and Gian Paolo Beretta}, doi = {10.1016/j.ijheatmasstransfer.2011.10.019}, year = {2012}, date = {2012-01-31}, journal = {International Journal of Heat and Mass Transfer}, volume = {55}, number = {4}, pages = {897-906}, abstract = {We report experimental evidence of a 20–40 % enhancement of the effective heat transfer coefficient for laminar flow of a partially miscible binary liquid–liquid mixture in a small diameter horizontal tube that obtains when phase separation occurs in the tube. A mixture of acetone–hexadecane is quenched into the two-phase region so as to induce spinodal decomposition. The heat transfer rate is enhanced by self-induced convective effects sustained by the free energy liberated during phase separation. The experimental heat transfer coefficients obtained when separation occurs are compared to the corresponding values predicted for flow of a hypothetic mixture with identical properties but undergoing separation. For such comparison, the energy balance equation must carefully take into account both the sensible heat and the excess enthalpy difference between the inlet and the outlet streams because our liquid–liquid binary mixture is a very asymmetric system with large excess enthalpies. The non-ideal mixture thermodynamic properties needed for the energy balance are obtained by an empirical procedure from the experimental data available in the literature for our mixture. The experimental setup and calculation procedure is tested by experiments performed using single-phase water flow and single-phase mixture flow (above the critical point). The convective heat transfer augmentation that results in the presence of liquid–liquid phase separation may be exploited in the cooling or heating of small scale systems where turbulent convection cannot be achieved.}, keywords = {Heat transfer enhancement, Spinodal decomposition}, pubstate = {published}, tppubtype = {article} } We report experimental evidence of a 20–40 % enhancement of the effective heat transfer coefficient for laminar flow of a partially miscible binary liquid–liquid mixture in a small diameter horizontal tube that obtains when phase separation occurs in the tube. A mixture of acetone–hexadecane is quenched into the two-phase region so as to induce spinodal decomposition. The heat transfer rate is enhanced by self-induced convective effects sustained by the free energy liberated during phase separation. The experimental heat transfer coefficients obtained when separation occurs are compared to the corresponding values predicted for flow of a hypothetic mixture with identical properties but undergoing separation. For such comparison, the energy balance equation must carefully take into account both the sensible heat and the excess enthalpy difference between the inlet and the outlet streams because our liquid–liquid binary mixture is a very asymmetric system with large excess enthalpies. The non-ideal mixture thermodynamic properties needed for the energy balance are obtained by an empirical procedure from the experimental data available in the literature for our mixture. The experimental setup and calculation procedure is tested by experiments performed using single-phase water flow and single-phase mixture flow (above the critical point). The convective heat transfer augmentation that results in the presence of liquid–liquid phase separation may be exploited in the cooling or heating of small scale systems where turbulent convection cannot be achieved. | |

57. | Beretta, Gian Paolo; Keck, James; Janbozorgi, Mohammad; Metghalchi, Hameed The Rate-Controlled Constrained-Equilibrium Approach to Far-From-Local-Equilibrium Thermodynamics Journal Article Entropy, 14 (2), pp. 92-130, 2012. Abstract | BibTeX | Tags: Chemical kinetics, Non-equilibrium and irreversible thermodynamics, Nonlinear dynamical systems, Nonlinear dynamics | Links: @article{Beretta_Keck_2012, title = {The Rate-Controlled Constrained-Equilibrium Approach to Far-From-Local-Equilibrium Thermodynamics}, author = {Gian Paolo Beretta and James C. Keck and Mohammad Janbozorgi and Hameed Metghalchi}, doi = {10.3390/e14020092}, year = {2012}, date = {2012-01-30}, journal = {Entropy}, volume = {14}, number = {2}, pages = {92-130}, abstract = {The Rate-Controlled Constrained-Equilibrium (RCCE) method for the description of the time-dependent behavior of dynamical systems in non-equilibrium states is a general, effective, physically based method for model order reduction that was originally developed in the framework of thermodynamics and chemical kinetics. A generalized mathematical formulation is presented here that allows including nonlinear constraints in non-local equilibrium systems characterized by the existence of a non-increasing Lyapunov functional under the system’s internal dynamics. The generalized formulation of RCCE enables to clarify the essentials of the method and the built-in general feature of thermodynamic consistency in the chemical kinetics context. In this paper, we work out the details of the method in a generalized mathematical-physics framework, but for definiteness we detail its well-known implementation in the traditional chemical kinetics framework. We detail proofs and spell out explicit functional dependences so as to bring out and clarify each underlying assumption of the method. In the standard context of chemical kinetics of ideal gas mixtures, we discuss the relations between the validity of the detailed balance condition off-equilibrium and the thermodynamic consistency of the method. We also discuss two examples of RCCE gas-phase combustion calculations to emphasize the constraint-dependent performance of the RCCE method.}, keywords = {Chemical kinetics, Non-equilibrium and irreversible thermodynamics, Nonlinear dynamical systems, Nonlinear dynamics}, pubstate = {published}, tppubtype = {article} } The Rate-Controlled Constrained-Equilibrium (RCCE) method for the description of the time-dependent behavior of dynamical systems in non-equilibrium states is a general, effective, physically based method for model order reduction that was originally developed in the framework of thermodynamics and chemical kinetics. A generalized mathematical formulation is presented here that allows including nonlinear constraints in non-local equilibrium systems characterized by the existence of a non-increasing Lyapunov functional under the system’s internal dynamics. The generalized formulation of RCCE enables to clarify the essentials of the method and the built-in general feature of thermodynamic consistency in the chemical kinetics context. In this paper, we work out the details of the method in a generalized mathematical-physics framework, but for definiteness we detail its well-known implementation in the traditional chemical kinetics framework. We detail proofs and spell out explicit functional dependences so as to bring out and clarify each underlying assumption of the method. In the standard context of chemical kinetics of ideal gas mixtures, we discuss the relations between the validity of the detailed balance condition off-equilibrium and the thermodynamic consistency of the method. We also discuss two examples of RCCE gas-phase combustion calculations to emphasize the constraint-dependent performance of the RCCE method. | |

## 2011 |
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56. | Foletti, Claudia; Farisè, Stefano; Grassi, Benedetta; Strazza, Domenico; Lancini, Matteo; Poesio, Pietro Experimental investigation on two-phase air-high viscosity oil flow in a horizontal pipe Journal Article Chemical Engineering Science, 66 (23), pp. 5968-5975, 2011. Abstract | BibTeX | Tags: Air–oil flow, Capacitance probe, Flow patterns maps, Highly viscous oil, Pressure drops | Links: @article{Foletti_Farisè_2011, title = {Experimental investigation on two-phase air-high viscosity oil flow in a horizontal pipe}, author = {Claudia Foletti and Stefano Farisè and Benedetta Grassi and Domenico Strazza and Matteo Lancini and Pietro Poesio}, doi = {10.1016/j.ces.2011.08.019}, year = {2011}, date = {2011-12-01}, journal = {Chemical Engineering Science}, volume = {66}, number = {23}, pages = {5968-5975}, abstract = {The flow of very-viscous-oil and air through a horizontal pipe (inner diameter 22 mm) is experimentally studied. We first build and analyze the flow pattern map; a comparison between the air–water and the air–oil flow pattern maps shows a strong influence of the fluid properties. The experimental flow maps are compared with empirical and theoretical ones – Baker (1954), Mandhane et al. (1974), and Petalas and Aziz (1998) – showing a poor agreement. Experimental pressure gradients are also reported and compared with theoretical model, but also in this case the agreement is not very satisfactory. Finally, the elongated bubble velocity and length are measured and compared to model present in the literature. We conclude that the high viscosity of the liquid phase has a strong influence on the results and that the current models are not able to predict the flow features satisfactorily.}, keywords = {Air–oil flow, Capacitance probe, Flow patterns maps, Highly viscous oil, Pressure drops}, pubstate = {published}, tppubtype = {article} } The flow of very-viscous-oil and air through a horizontal pipe (inner diameter 22 mm) is experimentally studied. We first build and analyze the flow pattern map; a comparison between the air–water and the air–oil flow pattern maps shows a strong influence of the fluid properties. The experimental flow maps are compared with empirical and theoretical ones – Baker (1954), Mandhane et al. (1974), and Petalas and Aziz (1998) – showing a poor agreement. Experimental pressure gradients are also reported and compared with theoretical model, but also in this case the agreement is not very satisfactory. Finally, the elongated bubble velocity and length are measured and compared to model present in the literature. We conclude that the high viscosity of the liquid phase has a strong influence on the results and that the current models are not able to predict the flow features satisfactorily. | |

55. | Demori, Marco; Ferrari, Vittorio; Poesio, Pietro; Strazza, Domenico A microfluidic capacitance sensor for fluid discrimination and characterization Journal Article Sensors and Actuators A: Physical, 172 (1), pp. 212-219, 2011. Abstract | BibTeX | Tags: Capacitive sensing, Fluid discrimination, Microfluidic devices, PDMS, Screen-printing technology | Links: @article{Demori_Ferrari_2011, title = {A microfluidic capacitance sensor for fluid discrimination and characterization}, author = {Marco Demori and Vittorio Ferrari and Pietro Poesio and Domenico Strazza}, doi = {10.1016/j.sna.2011.07.013}, year = {2011}, date = {2011-12-01}, journal = {Sensors and Actuators A: Physical}, volume = {172}, number = {1}, pages = {212-219}, abstract = {A microfluidic device with embedded capacitive sensing is proposed. The purpose of the device is fluid discrimination and characterization in a microchannel on the basis of the dielectric permittivity. The device is fabricated in a hybrid cost-effective technology which innovatively combines PDMS (PolyDiMethylSiloxane) soft photolithography and screen printing techniques. A microchannel, realized in a PDMS layer, is placed in the field of a sensing capacitor formed by electrodes screen-printed on a glass substrate. Fluids inside the microchannel affect the capacitance, that is in the order of femtofarads, which is measured by a tailored electronic interface system. The electronic system features a sensitivity of 100 V/pF and a resolution threshold of 0.06 fF. Experimental results obtained for different fluids injected in the microchannel demonstrate the ability of the system to discriminate the fluids and to estimate their dielectric permittivity both as pure samples and as mixtures at varying solute fractions. This makes the device a promising building block for fluid mixing monitoring in microfluidic systems.}, keywords = {Capacitive sensing, Fluid discrimination, Microfluidic devices, PDMS, Screen-printing technology}, pubstate = {published}, tppubtype = {article} } A microfluidic device with embedded capacitive sensing is proposed. The purpose of the device is fluid discrimination and characterization in a microchannel on the basis of the dielectric permittivity. The device is fabricated in a hybrid cost-effective technology which innovatively combines PDMS (PolyDiMethylSiloxane) soft photolithography and screen printing techniques. A microchannel, realized in a PDMS layer, is placed in the field of a sensing capacitor formed by electrodes screen-printed on a glass substrate. Fluids inside the microchannel affect the capacitance, that is in the order of femtofarads, which is measured by a tailored electronic interface system. The electronic system features a sensitivity of 100 V/pF and a resolution threshold of 0.06 fF. Experimental results obtained for different fluids injected in the microchannel demonstrate the ability of the system to discriminate the fluids and to estimate their dielectric permittivity both as pure samples and as mixtures at varying solute fractions. This makes the device a promising building block for fluid mixing monitoring in microfluidic systems. | |

54. | Strazza, Domenico; Demori, Marco; Ferrari, Vittorio; Poesio, Pietro Capacitance sensor for hold-up measurement in high-viscous-oil/conductive-water core-annular flows Journal Article Flow Measurement and Instrumentation, 22 (5), pp. 360-369, 2011. Abstract | BibTeX | Tags: Capacitance sensor, Capacitive instrumentation, Core-annular flow, Hold-up, Oil-water | Links: @article{Strazza_Demori_2011, title = {Capacitance sensor for hold-up measurement in high-viscous-oil/conductive-water core-annular flows}, author = {Domenico Strazza and Marco Demori and Vittorio Ferrari and Pietro Poesio}, doi = {10.1016/j.flowmeasinst.2011.04.008}, year = {2011}, date = {2011-10-01}, journal = {Flow Measurement and Instrumentation}, volume = {22}, number = {5}, pages = {360-369}, abstract = {Capacitance sensors are widely used in multiphase flows, for example, to estimate the hold-up in a given section of the pipe, taking advantage of the different permittivity values of the two liquids. The estimation is obtained by capacitance measurements between two electrodes, flush mounted on the external surface of the experimental pipe. Usually, capacitance sensors are used to investigate flows with non-conductive fluids, but they have the possibility to work also when, for example, conductive water is used. However, the capacitance technique applied to conductive fluids develops some issues. In this paper, we present a concave electrode sensor system developed for oil/conductive-water flows. A key contribution is to propose a modelization to the problem of capacitive sensing in presence of conductive fluids, based on a new approach to the parasitic couplings outside the measurement section. Thanks to this modelization, we propose a new design method for the working frequency and the electrode measurement head.}, keywords = {Capacitance sensor, Capacitive instrumentation, Core-annular flow, Hold-up, Oil-water}, pubstate = {published}, tppubtype = {article} } Capacitance sensors are widely used in multiphase flows, for example, to estimate the hold-up in a given section of the pipe, taking advantage of the different permittivity values of the two liquids. The estimation is obtained by capacitance measurements between two electrodes, flush mounted on the external surface of the experimental pipe. Usually, capacitance sensors are used to investigate flows with non-conductive fluids, but they have the possibility to work also when, for example, conductive water is used. However, the capacitance technique applied to conductive fluids develops some issues. In this paper, we present a concave electrode sensor system developed for oil/conductive-water flows. A key contribution is to propose a modelization to the problem of capacitive sensing in presence of conductive fluids, based on a new approach to the parasitic couplings outside the measurement section. Thanks to this modelization, we propose a new design method for the working frequency and the electrode measurement head. | |

53. | Strazza, Domenico; Grassi, Benedetta; Demori, Marco; Ferrari, Vittorio; Poesio, Pietro Core-annular flow in horizontal and slightly inclined pipes: Existence, pressure drops, and hold-up Journal Article Chemical Engineering Science, 66 (12), pp. 2853-2863, 2011. Abstract | BibTeX | Tags: Core-annular flow, Inclined flow, Oil–water, Pressure drops, Slip | Links: @article{Strazza_Grassi_2011, title = {Core-annular flow in horizontal and slightly inclined pipes: Existence, pressure drops, and hold-up}, author = {Domenico Strazza and Benedetta Grassi and Marco Demori and Vittorio Ferrari and Pietro Poesio}, doi = {10.1016/j.ces.2011.03.053}, year = {2011}, date = {2011-06-15}, journal = {Chemical Engineering Science}, volume = {66}, number = {12}, pages = {2853-2863}, abstract = {An analysis of high viscosity oil/water flow in horizontal and slightly inclined pipe is presented. We propose experimental flow maps – in particular we focus on the core-annular flow pattern boundary – pressure drops, and oil hold-up measurements. Experimental data are used to validate some models present in literature. Since hold-up measurement in liquid–liquid systems is particularly challenging and, therefore, only few data are available in literature, they are analyzed and commented in detail. The slip ratio computed by hold-up data is also provided and analyzed.}, keywords = {Core-annular flow, Inclined flow, Oil–water, Pressure drops, Slip}, pubstate = {published}, tppubtype = {article} } An analysis of high viscosity oil/water flow in horizontal and slightly inclined pipe is presented. We propose experimental flow maps – in particular we focus on the core-annular flow pattern boundary – pressure drops, and oil hold-up measurements. Experimental data are used to validate some models present in literature. Since hold-up measurement in liquid–liquid systems is particularly challenging and, therefore, only few data are available in literature, they are analyzed and commented in detail. The slip ratio computed by hold-up data is also provided and analyzed. | |

## 2010 |
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52. | Demori, Marco; Ferrari, Vittorio; Strazza, Domenico; Poesio, Pietro A capacitive sensor system for the analysis of two-phase flows of oil and conductive water Journal Article Sensors and Actuators A: Physical, 163 (1), pp. 172-179, 2010. Abstract | BibTeX | Tags: Capacitance probe, Capacitive sensor, Oil–water flow, Two-phase flow | Links: @article{Demori_Ferrari_2010, title = {A capacitive sensor system for the analysis of two-phase flows of oil and conductive water}, author = {Marco Demori and Vittorio Ferrari and Domenico Strazza and Pietro Poesio}, doi = {10.1016/j.sna.2010.08.018}, year = {2010}, date = {2010-09-01}, journal = {Sensors and Actuators A: Physical}, volume = {163}, number = {1}, pages = {172-179}, abstract = {A sensor system for the study of oil–water flow in pipes is proposed. The purpose is to estimate the area fraction occupied by each fluid in a given section of the pipe, taking advantage of the difference in dielectric permittivity between the fluids. The estimation is done by capacitance measurements between electrodes flush-mounted on the external surface of a nonconductive section of the pipe. A key contribution of the present work is to propose a solution to the problem of capacitive sensing in presence of conductive water which introduces parasitic coupling to stray elements outside the measurement section of the pipe. To this purpose it is proposed a novel sensor configuration that employs guard electrodes, coupled to a tailored electronic interface to drive the guard electrodes and amplify the measurement signal at 2 MHz. The sensor system has been designed, manufactured and tested in an experimental plant where flows of oil–tap water have been generated. The results obtained from the developed sensor system for different fluid fractions have been compared with those obtained by the Quick Closing Valve (QCV) technique adopted as a reference. Differences between the two methods below 3% have been found in the estimations of the normalized oil-area fraction.}, keywords = {Capacitance probe, Capacitive sensor, Oil–water flow, Two-phase flow}, pubstate = {published}, tppubtype = {article} } A sensor system for the study of oil–water flow in pipes is proposed. The purpose is to estimate the area fraction occupied by each fluid in a given section of the pipe, taking advantage of the difference in dielectric permittivity between the fluids. The estimation is done by capacitance measurements between electrodes flush-mounted on the external surface of a nonconductive section of the pipe. A key contribution of the present work is to propose a solution to the problem of capacitive sensing in presence of conductive water which introduces parasitic coupling to stray elements outside the measurement section of the pipe. To this purpose it is proposed a novel sensor configuration that employs guard electrodes, coupled to a tailored electronic interface to drive the guard electrodes and amplify the measurement signal at 2 MHz. The sensor system has been designed, manufactured and tested in an experimental plant where flows of oil–tap water have been generated. The results obtained from the developed sensor system for different fluid fractions have been compared with those obtained by the Quick Closing Valve (QCV) technique adopted as a reference. Differences between the two methods below 3% have been found in the estimations of the normalized oil-area fraction. | |

51. | Beretta, Gian Paolo Maximum entropy production rate in quantum thermodynamics Journal Article Journal of Physics: Conference Series, 237 (1), pp. 1-32, 2010. Abstract | BibTeX | Tags: entropy, quantum thermodinamics | Links: @article{Beretta_2010, title = {Maximum entropy production rate in quantum thermodynamics}, author = {Gian Paolo Beretta}, doi = {10.1088/1742-6596/237/1/012004}, year = {2010}, date = {2010-06-30}, booktitle = {Journal of Physics: Conference Series}, journal = {Journal of Physics: Conference Series}, volume = {237}, number = {1}, pages = {1-32}, abstract = {In the framework of the recent quest for well-behaved nonlinear extensions of the traditional Schrödinger-von Neumann unitary dynamics that could provide fundamental explanations of recent experimental evidence of loss of quantum coherence at the microscopic level, a recent paper [Gheorghiu-Svirschevski 2001 Phys. Rev. A 63 054102] reproposes the nonlinear equation of motion proposed by the present author [see Beretta G P 1987 Found. Phys. 17 365 and references therein] for quantum (thermo)dynamics of a single isolated indivisible constituent system, such as a single particle, qubit, qudit, spin or atomic system, or a Bose-Einstein or Fermi-Dirac field. As already proved, such nonlinear dynamics entails a fundamental unifying microscopic proof and extension of Onsager's reciprocity and Callen's fluctuation-dissipation relations to all nonequilibrium states, close and far from thermodynamic equilibrium. In this paper we propose a brief but self-contained review of the main results already proved, including the explicit geometrical construction of the equation of motion from the steepest-entropy-ascent ansatz and its exact mathematical and conceptual equivalence with the maximal-entropy-generation variational-principle formulation presented in Gheorghiu-Svirschevski S 2001 Phys. Rev. A 63 022105. Moreover, we show how it can be extended to the case of a composite system to obtain the general form of the equation of motion, consistent with the demanding requirements of strong separability and of compatibility with general thermodynamics principles. The irreversible term in the equation of motion describes the spontaneous attraction of the state operator in the direction of steepest entropy ascent, thus implementing the maximum entropy production principle in quantum theory. The time rate at which the path of steepest entropy ascent is followed has so far been left unspecified. As a step towards the identification of such rate, here we propose a possible, well-behaved and intriguing, general closure of the dynamics, compatible with the nontrivial requirements of strong separability. Based on the time–energy Heisenberg uncertainty relation, we derive a lower bound to the internal-relaxation-time functionals that determine the rate of entropy generation. This bound entails an upper bound to the rate of entropy generation. By this extreme maximal-entropy-generation-rate ansatz, each indivisible subsystem follows the direction of steepest locally perceived entropy ascent at the highest rate compatible with the time– energy uncertainty principle.}, keywords = {entropy, quantum thermodinamics}, pubstate = {published}, tppubtype = {article} } In the framework of the recent quest for well-behaved nonlinear extensions of the traditional Schrödinger-von Neumann unitary dynamics that could provide fundamental explanations of recent experimental evidence of loss of quantum coherence at the microscopic level, a recent paper [Gheorghiu-Svirschevski 2001 Phys. Rev. A 63 054102] reproposes the nonlinear equation of motion proposed by the present author [see Beretta G P 1987 Found. Phys. 17 365 and references therein] for quantum (thermo)dynamics of a single isolated indivisible constituent system, such as a single particle, qubit, qudit, spin or atomic system, or a Bose-Einstein or Fermi-Dirac field. As already proved, such nonlinear dynamics entails a fundamental unifying microscopic proof and extension of Onsager's reciprocity and Callen's fluctuation-dissipation relations to all nonequilibrium states, close and far from thermodynamic equilibrium. In this paper we propose a brief but self-contained review of the main results already proved, including the explicit geometrical construction of the equation of motion from the steepest-entropy-ascent ansatz and its exact mathematical and conceptual equivalence with the maximal-entropy-generation variational-principle formulation presented in Gheorghiu-Svirschevski S 2001 Phys. Rev. A 63 022105. Moreover, we show how it can be extended to the case of a composite system to obtain the general form of the equation of motion, consistent with the demanding requirements of strong separability and of compatibility with general thermodynamics principles. The irreversible term in the equation of motion describes the spontaneous attraction of the state operator in the direction of steepest entropy ascent, thus implementing the maximum entropy production principle in quantum theory. The time rate at which the path of steepest entropy ascent is followed has so far been left unspecified. As a step towards the identification of such rate, here we propose a possible, well-behaved and intriguing, general closure of the dynamics, compatible with the nontrivial requirements of strong separability. Based on the time–energy Heisenberg uncertainty relation, we derive a lower bound to the internal-relaxation-time functionals that determine the rate of entropy generation. This bound entails an upper bound to the rate of entropy generation. By this extreme maximal-entropy-generation-rate ansatz, each indivisible subsystem follows the direction of steepest locally perceived entropy ascent at the highest rate compatible with the time– energy uncertainty principle. | |

50. | Zanchini, Enzo; Beretta, Gian Paolo Removing heat and conceptual loops from the definition of entropy Journal Article International Journal of Thermodynamics, 13 (2), pp. 67-76, 2010. Abstract | BibTeX | Tags: entropy | Links: @article{Zanchini_Beretta_2010, title = {Removing heat and conceptual loops from the definition of entropy}, author = {Enzo Zanchini and Gian Paolo Beretta}, doi = {10.5541/ijot.1034000283}, year = {2010}, date = {2010-05-01}, journal = {International Journal of Thermodynamics}, volume = {13}, number = {2}, pages = {67-76}, abstract = {A rigorous and general logical scheme is presented, which provides an operative non-statistical definition of entropy valid also in the nonequilibrium domain and free of the usual conceptual loops and unnecessary assumptions that restrict the traditional definition of entropy to the equilibrium domain. The scheme is based on carefully worded operative definitions for all the fundamental concepts employed, including those of system, state of a system, isolated system, separable system, systems uncorrelated form each other, environment of a system, process and reversible process. The treatment considers also systems with movable internal walls and/or semipermeable walls, with chemical reactions and and/or external force fields, and with small numbers of particles. The definition of entropy involves neither the concept of heat nor that of quasistatic process; it applies to both equilibrium and nonequilibrium states. Simple and rigorous proofs of the additivity of entropy and of the principle of entropy nondecrease complete the logical framework.}, keywords = {entropy}, pubstate = {published}, tppubtype = {article} } A rigorous and general logical scheme is presented, which provides an operative non-statistical definition of entropy valid also in the nonequilibrium domain and free of the usual conceptual loops and unnecessary assumptions that restrict the traditional definition of entropy to the equilibrium domain. The scheme is based on carefully worded operative definitions for all the fundamental concepts employed, including those of system, state of a system, isolated system, separable system, systems uncorrelated form each other, environment of a system, process and reversible process. The treatment considers also systems with movable internal walls and/or semipermeable walls, with chemical reactions and and/or external force fields, and with small numbers of particles. The definition of entropy involves neither the concept of heat nor that of quasistatic process; it applies to both equilibrium and nonequilibrium states. Simple and rigorous proofs of the additivity of entropy and of the principle of entropy nondecrease complete the logical framework. | |

## 2009 |
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49. | Poesio, Pietro; Beretta, Gian Paolo; Thorsen, Todd Dissolution of a liquid microdroplet in a nonideal liquid-liquid mixture far from thermodynamic equilibrium Journal Article Physical Review Letters, 103 (6), pp. 064501, 2009. Abstract | BibTeX | Tags: dissolution, micro-droplet, non-ideal | Links: @article{Poesio_Beretta_2009, title = {Dissolution of a liquid microdroplet in a nonideal liquid-liquid mixture far from thermodynamic equilibrium}, author = {Pietro Poesio and Gian Paolo Beretta and Todd Thorsen}, editor = {American Physical Society}, doi = {10.1103/PhysRevLett.103.064501}, year = {2009}, date = {2009-08-05}, journal = {Physical Review Letters}, volume = {103}, number = {6}, pages = {064501}, abstract = {A droplet placed in a liquid-liquid solution is expected to grow, or shrink, in time as ∼t1/2. In this Letter, we report experimental evidence that when the composition in the interface is far from thermodynamic equilibrium due to the nonideality of the mixture, a droplet shrinks as ∼t. This scaling is due to the coupling between mass and momentum transfer known as Korteweg forces as a result of which the droplet self-propels around. The consequent hydrodynamic convection greatly enhances the mass transfer between the droplet and the bulk phase. Thus, the combined effect of nonideality and nonequilibrium modifies the dynamical behavior of the dissolving droplet.}, keywords = {dissolution, micro-droplet, non-ideal}, pubstate = {published}, tppubtype = {article} } A droplet placed in a liquid-liquid solution is expected to grow, or shrink, in time as ∼t1/2. In this Letter, we report experimental evidence that when the composition in the interface is far from thermodynamic equilibrium due to the nonideality of the mixture, a droplet shrinks as ∼t. This scaling is due to the coupling between mass and momentum transfer known as Korteweg forces as a result of which the droplet self-propels around. The consequent hydrodynamic convection greatly enhances the mass transfer between the droplet and the bulk phase. Thus, the combined effect of nonideality and nonequilibrium modifies the dynamical behavior of the dissolving droplet. | |

48. | Beretta, Gian Paolo Nonlinear quantum evolution equations to model irreversible adiabatic relaxation with maximal entropy production and other nonunitary processes Journal Article Reports on Mathematical Physics, 64 , pp. 139-168, 2009. Abstract | BibTeX | Tags: entropy, irreversible adiabatic relaxation, nonunitary process, quantum thermodinamics | Links: @article{Beretta_2009, title = {Nonlinear quantum evolution equations to model irreversible adiabatic relaxation with maximal entropy production and other nonunitary processes}, author = {Gian Paolo Beretta}, doi = {10.1016/S0034-4877(09)90024-6}, year = {2009}, date = {2009-06-30}, journal = {Reports on Mathematical Physics}, volume = {64}, pages = {139-168}, abstract = {We first discuss the geometrical construction and the main mathematical features of the maximum-entropy-production/steepest-entropy-ascent nonlinear evolution equation proposed long ago by this author in the framework of a fully quantum theory of irreversibility and thermodynamics for a single isolated or adiabatic particle, qubit, or qudit, and recently rediscovered by other authors. The nonlinear equation generates a dynamical group, not just a semigroup, providing a deterministic description of irreversible conservative relaxation towards equilibrium from any non-equilibrium density operator. It satisfies a very restrictive stability requirement equivalent to the Hatsopoulos-Keenan statement of the second law of thermodynamics. We then examine the form of the evolution equation we proposed to describe multipartite isolated or adiabatic systems. This hinges on novel nonlinear projections defining local operators that we interpret as ``local perceptions'' of the overall system's energy and entropy. Each component particle contributes an independent local tendency along the direction of steepest increase of the locally perceived entropy at constant locally perceived energy. It conserves both the locally-perceived energies and the overall energy, and meets strong separability and non-signaling conditions, even though the local evolutions are not independent of existing correlations. We finally show how the geometrical construction can readily lead to other thermodynamically relevant models, such as of the nonunitary isoentropic evolution needed for full extraction of a system's adiabatic availability.}, keywords = {entropy, irreversible adiabatic relaxation, nonunitary process, quantum thermodinamics}, pubstate = {published}, tppubtype = {article} } We first discuss the geometrical construction and the main mathematical features of the maximum-entropy-production/steepest-entropy-ascent nonlinear evolution equation proposed long ago by this author in the framework of a fully quantum theory of irreversibility and thermodynamics for a single isolated or adiabatic particle, qubit, or qudit, and recently rediscovered by other authors. The nonlinear equation generates a dynamical group, not just a semigroup, providing a deterministic description of irreversible conservative relaxation towards equilibrium from any non-equilibrium density operator. It satisfies a very restrictive stability requirement equivalent to the Hatsopoulos-Keenan statement of the second law of thermodynamics. We then examine the form of the evolution equation we proposed to describe multipartite isolated or adiabatic systems. This hinges on novel nonlinear projections defining local operators that we interpret as ``local perceptions'' of the overall system's energy and entropy. Each component particle contributes an independent local tendency along the direction of steepest increase of the locally perceived entropy at constant locally perceived energy. It conserves both the locally-perceived energies and the overall energy, and meets strong separability and non-signaling conditions, even though the local evolutions are not independent of existing correlations. We finally show how the geometrical construction can readily lead to other thermodynamically relevant models, such as of the nonunitary isoentropic evolution needed for full extraction of a system's adiabatic availability. | |

47. | Poesio, Pietro; Strazza, Domenico; Sotgia, Giorgio Very-viscous-oil/water/air flow through horizontal pipes: Pressure drop measurement and prediction Journal Article Chemical Engineering Science, 64 (6), pp. 1136-1142, 2009. Abstract | BibTeX | Tags: multiphase flow, oil-water-air, Pressure drops, viscous fluid flow | Links: @article{Poesio_Strazza_2009, title = {Very-viscous-oil/water/air flow through horizontal pipes: Pressure drop measurement and prediction}, author = {Pietro Poesio and Domenico Strazza and Giorgio Sotgia}, editor = {Elsevier}, doi = {10.1016/j.ces.2008.10.061}, year = {2009}, date = {2009-03-16}, journal = {Chemical Engineering Science}, volume = {64}, number = {6}, pages = {1136-1142}, abstract = {Core annular flow pattern, where a low viscosity liquid surrounds a very-viscous one, may be very interesting for heavy oil transportation. However, in oil production, oil and water rarely flow alone and gas is usually present. Despite several publications on liquid–liquid core annular flow, no much work has been done towards a proper characterization of the effect of gas on pressure drop. The aim of this paper is twofold: to provide a new data base on three-phase (very-viscous-oil/water/air) flow, and to propose a simple model for the determination of pressure drop.}, keywords = {multiphase flow, oil-water-air, Pressure drops, viscous fluid flow}, pubstate = {published}, tppubtype = {article} } Core annular flow pattern, where a low viscosity liquid surrounds a very-viscous one, may be very interesting for heavy oil transportation. However, in oil production, oil and water rarely flow alone and gas is usually present. Despite several publications on liquid–liquid core annular flow, no much work has been done towards a proper characterization of the effect of gas on pressure drop. The aim of this paper is twofold: to provide a new data base on three-phase (very-viscous-oil/water/air) flow, and to propose a simple model for the determination of pressure drop. | |

46. | Poesio, Pietro; Ooms, Gijs Fouling by external particles and ultrasonic cleaning of a porous material Journal Article SPE Journal, 14 (1), pp. 14-29, 2009. Abstract | BibTeX | Tags: porous material, ultrasonic cleaning | Links: @article{Poesio_Ooms_2009, title = {Fouling by external particles and ultrasonic cleaning of a porous material}, author = {Pietro Poesio and Gijs Ooms}, doi = {10.2118/100812-PA}, year = {2009}, date = {2009-03-01}, journal = {SPE Journal}, volume = {14}, number = {1}, pages = {14-29}, abstract = {The aim of this paper is to investigate experimentally the fouling of a porous material by external particles and the optimal way to clean the porous material with high-frequency acoustic waves. In particular, we are interested in the fouling by mud particles of the near-wellbore region of an oil reservoir. In the experiments, therefore, we used natural sandstone as porous material and mud particles as fouling particles. To generate fouling, mud particles were flushed through a sandstone core. Next, the core was treated with very short bursts of ultrasound, and the change in permeability was measured after each burst. (Earlier papers report only the end result after applying the total amount of acoustic energy.) Experiments were carried out under different acoustic-cleaning conditions to investigate the influence of the relevant parameters on the cleaning process. For instance, the amplitude of the acoustic waves, the duration of the bursts, and the time between the bursts were varied. During the ultrasonic-cleaning process, brine flowed through the core. The effect of this flow was studied by changing the flow rate. Also, the effect of the temperature, pressure, and initial core permeability on the cleaning process was investigated. The experimental results show that short bursts of acoustic energy are more efficient for cleaning than long bursts or continuous application of ultrasound (for the same total amount of acoustic energy). The overall conclusion is that the optimal method of ultrasonic cleaning is to apply many very short bursts of low-amplitude acoustic energy, with a short rest time between the bursts while keeping the liquid (brine) flow at a very low velocity. More acoustic energy is needed to clean a core with a high initial permeability than a core with a low initial permeability. At low pressure, cavitation occurs and prevents the generation of ultrasonic bursts. Cavitation can even have a negative effect on the cleaning process.}, keywords = {porous material, ultrasonic cleaning}, pubstate = {published}, tppubtype = {article} } The aim of this paper is to investigate experimentally the fouling of a porous material by external particles and the optimal way to clean the porous material with high-frequency acoustic waves. In particular, we are interested in the fouling by mud particles of the near-wellbore region of an oil reservoir. In the experiments, therefore, we used natural sandstone as porous material and mud particles as fouling particles. To generate fouling, mud particles were flushed through a sandstone core. Next, the core was treated with very short bursts of ultrasound, and the change in permeability was measured after each burst. (Earlier papers report only the end result after applying the total amount of acoustic energy.) Experiments were carried out under different acoustic-cleaning conditions to investigate the influence of the relevant parameters on the cleaning process. For instance, the amplitude of the acoustic waves, the duration of the bursts, and the time between the bursts were varied. During the ultrasonic-cleaning process, brine flowed through the core. The effect of this flow was studied by changing the flow rate. Also, the effect of the temperature, pressure, and initial core permeability on the cleaning process was investigated. The experimental results show that short bursts of acoustic energy are more efficient for cleaning than long bursts or continuous application of ultrasound (for the same total amount of acoustic energy). The overall conclusion is that the optimal method of ultrasonic cleaning is to apply many very short bursts of low-amplitude acoustic energy, with a short rest time between the bursts while keeping the liquid (brine) flow at a very low velocity. More acoustic energy is needed to clean a core with a high initial permeability than a core with a low initial permeability. At low pressure, cavitation occurs and prevents the generation of ultrasonic bursts. Cavitation can even have a negative effect on the cleaning process. | |

45. | Poesio, Pietro; Sotgia, Giorgio; Strazza, Domenico Experimental investigation of three-phase mixtures of oil-water-air through a pipeline Journal Article Multiphase Science and Technology, 21 (1-2), pp. 107-122, 2009. Abstract | BibTeX | Tags: oil-water-air, Three-phase flows | Links: @article{Poesio_Sotgia_2009, title = {Experimental investigation of three-phase mixtures of oil-water-air through a pipeline}, author = {Pietro Poesio and Giorgio Sotgia and Domenico Strazza}, doi = {10.1615/MultScienTechn.v21.i1-2.90}, year = {2009}, date = {2009-01-01}, journal = {Multiphase Science and Technology}, volume = {21}, number = {1-2}, pages = {107-122}, abstract = {A three-phase flow of oil, water, and gas through a pipeline often occurs in industry. It is important to study such flows in order to be able to design a three-phase flow pipeline. To that purpose, experiments with oil, water, and air in a 28- and a 40-mm i.d. glass pipe were carried out to derive a new data set for a three-phase flow in a horizontal pipeline. First, we investigated the pressure drop, showing the influence of air injection on the two-phase flow reference flow pattern. We found a strong link between the qualitative behavior of the three-phase pressure drop reduction factor and the two-phase flow reference flow pattern. Finally, we studied the dynamic characteristics of the elongated air bubbles, analyzing both the bubble frequency and velocity.}, keywords = {oil-water-air, Three-phase flows}, pubstate = {published}, tppubtype = {article} } A three-phase flow of oil, water, and gas through a pipeline often occurs in industry. It is important to study such flows in order to be able to design a three-phase flow pipeline. To that purpose, experiments with oil, water, and air in a 28- and a 40-mm i.d. glass pipe were carried out to derive a new data set for a three-phase flow in a horizontal pipeline. First, we investigated the pressure drop, showing the influence of air injection on the two-phase flow reference flow pattern. We found a strong link between the qualitative behavior of the three-phase pressure drop reduction factor and the two-phase flow reference flow pattern. Finally, we studied the dynamic characteristics of the elongated air bubbles, analyzing both the bubble frequency and velocity. | |

## 2008 |
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44. | Beretta, Gian Paolo The devil is in the Details Journal Article Physics Today, 61 , pp. 57, 2008. BibTeX | Tags: quantum | Links: @article{Beretta_Scully_2008, title = {The devil is in the Details }, author = {Gian Paolo Beretta}, doi = {10.1063/1.3027993}, year = {2008}, date = {2008-11-01}, journal = {Physics Today}, volume = {61}, pages = {57}, keywords = {quantum}, pubstate = {published}, tppubtype = {article} } | |

43. | Grassi, Benedetta; Strazza, Domenico; Poesio, Pietro Experimental validation of theoretical models in two-phase high-viscosity ratio liquid–liquid flows in horizontal and slightly inclined pipes Journal Article International Journal of Multiphase Flow, 34 (10), pp. 950-965, 2008. Abstract | BibTeX | Tags: Flow pattern, Highly viscous oil, Oil-water, Pressure drops | Links: @article{Grassi_Strazza_2009, title = {Experimental validation of theoretical models in two-phase high-viscosity ratio liquid–liquid flows in horizontal and slightly inclined pipes}, author = {Benedetta Grassi and Domenico Strazza and Pietro Poesio}, doi = {10.1016/j.ijmultiphaseflow.2008.03.006}, year = {2008}, date = {2008-10-01}, journal = {International Journal of Multiphase Flow}, volume = {34}, number = {10}, pages = {950-965}, abstract = {Liquid–liquid flow literature proposes models developed to predict quantities and phenomena of interest, once given fluid properties and the features of the flow domain. The validity of any model should be verified through experimental observations, being this practice an effective way to evaluate the model conditions of applicability and possible limitations. Despite the fact that several works have already been proposed on the validation of theoretical models, most of them concern liquids characterised by low viscosity ratio View the MathML source, while in industrial realities (such as petroleum or food ones) the liquids involved are often characterised by high viscosity ratios. The extension of low-View the MathML source results to high-View the MathML source flows is not straightforward, so that it is necessary to validate the models for the latter case specifically. This work presents experimental pressure drops and flow-pattern maps associated to the flow of oil and water in horizontal and slightly inclined pipe, where the chosen liquids are characterised by an oil-to-water viscosity ratio of about 800:1 at 20 °C. Various theoretical models have been considered, with particular attention to core-annular flow two-fluid model and oil-in-water dispersion homogeneous no-slip model for the prediction of associated pressure drops, and flow-pattern map transition criteria involving the regimes encountered in the experimental tests. The theoretical predictions have been then compared to the experimental results. A satisfactory agreement has been found especially as concerns pressure drop comparisons. As regards the predicted transition boundaries superimposed on the corresponding flow-pattern maps, the ‘free’ parameters have been fitted on the basis of experimental results and observations, and the final agreement is good in the prediction of both the core-annular flow region of existence and the transition to oil-in-water dispersion. No conclusion can be expressed on transition criteria involving stratified flow, which only seldom has been observed in the performed experiments.}, keywords = {Flow pattern, Highly viscous oil, Oil-water, Pressure drops}, pubstate = {published}, tppubtype = {article} } Liquid–liquid flow literature proposes models developed to predict quantities and phenomena of interest, once given fluid properties and the features of the flow domain. The validity of any model should be verified through experimental observations, being this practice an effective way to evaluate the model conditions of applicability and possible limitations. Despite the fact that several works have already been proposed on the validation of theoretical models, most of them concern liquids characterised by low viscosity ratio View the MathML source, while in industrial realities (such as petroleum or food ones) the liquids involved are often characterised by high viscosity ratios. The extension of low-View the MathML source results to high-View the MathML source flows is not straightforward, so that it is necessary to validate the models for the latter case specifically. This work presents experimental pressure drops and flow-pattern maps associated to the flow of oil and water in horizontal and slightly inclined pipe, where the chosen liquids are characterised by an oil-to-water viscosity ratio of about 800:1 at 20 °C. Various theoretical models have been considered, with particular attention to core-annular flow two-fluid model and oil-in-water dispersion homogeneous no-slip model for the prediction of associated pressure drops, and flow-pattern map transition criteria involving the regimes encountered in the experimental tests. The theoretical predictions have been then compared to the experimental results. A satisfactory agreement has been found especially as concerns pressure drop comparisons. As regards the predicted transition boundaries superimposed on the corresponding flow-pattern maps, the ‘free’ parameters have been fitted on the basis of experimental results and observations, and the final agreement is good in the prediction of both the core-annular flow region of existence and the transition to oil-in-water dispersion. No conclusion can be expressed on transition criteria involving stratified flow, which only seldom has been observed in the performed experiments. | |

42. | Beretta, Gian Paolo Modeling non-equilibrium dynamics of a discrete probability distribution: general rate equation for maximal entropy generation in a maximum-entropy landscape with time-dependent constraints Journal Article Entropy, 10 (3), pp. 160-182, 2008. Abstract | BibTeX | Tags: Fluctuation-dissipation, irreversible thermodynamics, maximum entropy, nonequilibrium dynamics, Nonlinear dynamical systems, Onsager reciprocity, steepest-entropy-ascent | Links: @article{Beretta_2008, title = {Modeling non-equilibrium dynamics of a discrete probability distribution: general rate equation for maximal entropy generation in a maximum-entropy landscape with time-dependent constraints}, author = {Gian Paolo Beretta}, doi = {10.3390/entropy-e10030010}, year = {2008}, date = {2008-08-14}, journal = {Entropy}, volume = {10}, number = {3}, pages = {160-182}, abstract = {A rate equation for a discrete probability distribution is discussed as a route to describe smooth relaxation towards the maximum entropy distribution compatible at all times with one or more linear constraints. The resulting dynamics follows the path of steepest entropy ascent compatible with the constraints. The rate equation is consistent with the Onsager theorem of reciprocity and the fluctuation-dissipation theorem. The mathematical formalism was originally developed to obtain a quantum theoretical unification of mechanics and thermodinamics. It is presented here in a general, non-quantal formulation as a part of an effort to develop tools for the phenomenological treatment of non-equilibrium problems with applications in engineering, biology, sociology, and economics. The rate equation is also extended to include the case of assigned time-dependences of the constraints and the entropy, such as for modeling non-equilibrium energy and entropy exchanges. }, keywords = {Fluctuation-dissipation, irreversible thermodynamics, maximum entropy, nonequilibrium dynamics, Nonlinear dynamical systems, Onsager reciprocity, steepest-entropy-ascent}, pubstate = {published}, tppubtype = {article} } A rate equation for a discrete probability distribution is discussed as a route to describe smooth relaxation towards the maximum entropy distribution compatible at all times with one or more linear constraints. The resulting dynamics follows the path of steepest entropy ascent compatible with the constraints. The rate equation is consistent with the Onsager theorem of reciprocity and the fluctuation-dissipation theorem. The mathematical formalism was originally developed to obtain a quantum theoretical unification of mechanics and thermodinamics. It is presented here in a general, non-quantal formulation as a part of an effort to develop tools for the phenomenological treatment of non-equilibrium problems with applications in engineering, biology, sociology, and economics. The rate equation is also extended to include the case of assigned time-dependences of the constraints and the entropy, such as for modeling non-equilibrium energy and entropy exchanges. | |

41. | Poesio, Pietro; Beretta, Gian Paolo Minimal dissipation rate approach to correlate phase inversion data Journal Article International Journal of Multiphase Flow, 34 (7), pp. 684-689, 2008. Abstract | BibTeX | Tags: minimal dissipation rate, oil-water mixtures, phase inversion | Links: @article{Poesio_Beretta_2008, title = {Minimal dissipation rate approach to correlate phase inversion data}, author = {Pietro Poesio and Gian Paolo Beretta}, doi = {10.1016/j.ijmultiphaseflow.2007.12.006}, year = {2008}, date = {2008-07-01}, journal = {International Journal of Multiphase Flow}, volume = {34}, number = {7}, pages = {684-689}, abstract = {Phase inversion refers to the phenomenon whereby a small change in operational flow conditions causes an oil-in-water dispersed flow pattern to suddenly switch to a water-in-oil flow pattern, and viceversa. This paper proposes an interpretation of phase inversion in terms of minimal dissipation rate. To this end, the dissipation rate is computed by a simple homogeneous model together with available correlations for effective viscosity in dispersed flows. It is shown that the data available in the literature can be reasonably interpreted as a manifestation of minimal dissipation rate. Furthermore, if the assumed effective viscosity correlations take into account pipe wettability, the minimal dissipation rate approach is capable to interpret also the so-called ambivalent range (hysteresis effect) and correlate the available data.}, keywords = {minimal dissipation rate, oil-water mixtures, phase inversion}, pubstate = {published}, tppubtype = {article} } Phase inversion refers to the phenomenon whereby a small change in operational flow conditions causes an oil-in-water dispersed flow pattern to suddenly switch to a water-in-oil flow pattern, and viceversa. This paper proposes an interpretation of phase inversion in terms of minimal dissipation rate. To this end, the dissipation rate is computed by a simple homogeneous model together with available correlations for effective viscosity in dispersed flows. It is shown that the data available in the literature can be reasonably interpreted as a manifestation of minimal dissipation rate. Furthermore, if the assumed effective viscosity correlations take into account pipe wettability, the minimal dissipation rate approach is capable to interpret also the so-called ambivalent range (hysteresis effect) and correlate the available data. | |

40. | Beretta, Gian Paolo Axiomatic definition of entropy for nonequilibrium states Journal Article International Journal of Thermodynamics, 11 (2), pp. 39-48, 2008. Abstract | BibTeX | Tags: axiomatic foundations of thermodynamics, entropy, nonequilibrium entropy, second law | Links: @article{Beretta_axiomatic_2008, title = {Axiomatic definition of entropy for nonequilibrium states }, author = {Gian Paolo Beretta}, doi = {10.5541/ijot.1034000211}, year = {2008}, date = {2008-06-01}, journal = {International Journal of Thermodynamics}, volume = {11}, number = {2}, pages = {39-48}, abstract = {In introductory courses and textbooks on elementary thermodynamics, entropy is often presented as a property defined only for equilibrium states, and its axiomatic definition is almost invariably given in terms of a heat to temperature ratio, the traditional Clausius definition. Teaching thermodynamics to undergraduate and graduate students from all over the globe, we have sensed a need for more clarity, unambiguity, generality and logical consistency in the exposition of thermodynamics, including the general definition of entropy, than provided by traditional approaches. Continuing the effort pioneered by Keenan and Hatsopoulos in 1965, we proposed in 1991 a novel axiomatic approach which eliminates the ambiguities, logical circularities and inconsistencies of the traditional approach still adopted in many new books. One of the new and important aspects of our exposition is the simple, non-mathematical axiomatic definition of entropy which naturally extends the traditional Clausius definition to all states, including non-equilibrium states (for which temperature is not defined). And it does so without any recourse to statistical mechanical reasoning. We have successfully presented the foundations of thermodynamics in undergraduate and graduate courses for the past thirty years. Our approach, including the definition of entropy for non-equilibrium states, is developed with full proofs in the treatise E. P. Gyftopoulos and G. P. Beretta, Thermodynamics. Foundations and Applications, Dover Edition, 2005 (First edition, Macmillan, 1991) [1]. The slight variation we present here illustrates and emphasizes the essential elements and the minimal logical sequence to get as quickly as possible to our general axiomatic definition of entropy valid for nonequilibrium states no matter how "far" from thermodynamic equilibrium.}, keywords = {axiomatic foundations of thermodynamics, entropy, nonequilibrium entropy, second law}, pubstate = {published}, tppubtype = {article} } In introductory courses and textbooks on elementary thermodynamics, entropy is often presented as a property defined only for equilibrium states, and its axiomatic definition is almost invariably given in terms of a heat to temperature ratio, the traditional Clausius definition. Teaching thermodynamics to undergraduate and graduate students from all over the globe, we have sensed a need for more clarity, unambiguity, generality and logical consistency in the exposition of thermodynamics, including the general definition of entropy, than provided by traditional approaches. Continuing the effort pioneered by Keenan and Hatsopoulos in 1965, we proposed in 1991 a novel axiomatic approach which eliminates the ambiguities, logical circularities and inconsistencies of the traditional approach still adopted in many new books. One of the new and important aspects of our exposition is the simple, non-mathematical axiomatic definition of entropy which naturally extends the traditional Clausius definition to all states, including non-equilibrium states (for which temperature is not defined). And it does so without any recourse to statistical mechanical reasoning. We have successfully presented the foundations of thermodynamics in undergraduate and graduate courses for the past thirty years. Our approach, including the definition of entropy for non-equilibrium states, is developed with full proofs in the treatise E. P. Gyftopoulos and G. P. Beretta, Thermodynamics. Foundations and Applications, Dover Edition, 2005 (First edition, Macmillan, 1991) [1]. The slight variation we present here illustrates and emphasizes the essential elements and the minimal logical sequence to get as quickly as possible to our general axiomatic definition of entropy valid for nonequilibrium states no matter how "far" from thermodynamic equilibrium. | |

39. | Poesio, Pietro Experimental determination of pressure drop and statistical properties of oil-water intermittent flow through horizontal pipe Journal Article Experimental Thermal and Fluid Science, 32 (8), pp. 1523-1529, 2008. Abstract | BibTeX | Tags: horizontal pipe, Oil-water, Pressure drops | Links: @article{Poesio2008, title = {Experimental determination of pressure drop and statistical properties of oil-water intermittent flow through horizontal pipe}, author = {Pietro Poesio}, doi = {10.1016/j.expthermflusci.2008.04.009}, year = {2008}, date = {2008-05-08}, journal = {Experimental Thermal and Fluid Science}, volume = {32}, number = {8}, pages = {1523-1529}, abstract = {In this paper, oil-water slug flow is studied experimentally. After presenting the experimental set-up and the post-processing tools, flow maps and pressure drops are shown. The main focus of this piece of work is, however, the determination of the statistical behaviour of the elongated oil drops. The characteristic frequency of the process is determined by three estimators: the mean frequency, the most probable frequency, and the so-called diffusional frequency. All the tools give very similar results indicating a regular behaviour of the flow. The regularity was then further proved by means of both diffusional analysis and by the rescaled range analysis. The fractal dimension of the process was also estimated reinforcing again the conclusion that the flow is made up by highly coherent structures.}, keywords = {horizontal pipe, Oil-water, Pressure drops}, pubstate = {published}, tppubtype = {article} } In this paper, oil-water slug flow is studied experimentally. After presenting the experimental set-up and the post-processing tools, flow maps and pressure drops are shown. The main focus of this piece of work is, however, the determination of the statistical behaviour of the elongated oil drops. The characteristic frequency of the process is determined by three estimators: the mean frequency, the most probable frequency, and the so-called diffusional frequency. All the tools give very similar results indicating a regular behaviour of the flow. The regularity was then further proved by means of both diffusional analysis and by the rescaled range analysis. The fractal dimension of the process was also estimated reinforcing again the conclusion that the flow is made up by highly coherent structures. | |

38. | Poesio, Pietro Walsh spectral analysis of binary signals arising from intermittent two-phase flows Journal Article International Journal of Multiphase Flow, 34 (5), pp. 516-522, 2008. BibTeX | Tags: binary signals, spectral analysis, Two-phase flow | Links: @article{Poesio_2008, title = {Walsh spectral analysis of binary signals arising from intermittent two-phase flows}, author = {Pietro Poesio}, doi = {10.1016/j.ijmultiphaseflow.2007.10.007}, year = {2008}, date = {2008-05-01}, journal = {International Journal of Multiphase Flow}, volume = {34}, number = {5}, pages = {516-522}, keywords = {binary signals, spectral analysis, Two-phase flow}, pubstate = {published}, tppubtype = {article} } | |

37. | Ooms, Gijs; Poelma, Christian; Poesio, Pietro; Pourquie, Mathieu; Westerweel, Jerry Verification of a model to predict the influence of particle inertia and gravity on a decaying turbulent particle-laden flow Journal Article International Journal of Multiphase Flow, 34 (1), pp. 29-41, 2008. Abstract | BibTeX | Tags: decaying turbulence, experimental verification, particles, Theoretical model, two-way coupling | Links: @article{Ooms_Poelma_Poesio_2008, title = {Verification of a model to predict the influence of particle inertia and gravity on a decaying turbulent particle-laden flow}, author = {Gijs Ooms and Christian Poelma and Pietro Poesio and Mathieu J. B. M. Pourquie and Jerry Westerweel}, doi = {10.1016/j.ijmultiphaseflow.2007.08.002}, year = {2008}, date = {2008-01-01}, journal = {International Journal of Multiphase Flow}, volume = {34}, number = {1}, pages = {29-41}, abstract = {In an earlier publication some of the authors presented a theoretical model for the calculation of the influence of particle inertia and gravity on the turbulence in a stationary particle-laden flow. In the present publication the model is extended for application to a decaying suspension. Also a comparison is given between predictions made with the model and experimental data (own data and data reported in the literature) on a decaying turbulent flow with particles in a water tunnel or in a wind tunnel. For most of the experiments a prediction with reasonable accuracy and an interpretation is possible by means of the model.}, keywords = {decaying turbulence, experimental verification, particles, Theoretical model, two-way coupling}, pubstate = {published}, tppubtype = {article} } In an earlier publication some of the authors presented a theoretical model for the calculation of the influence of particle inertia and gravity on the turbulence in a stationary particle-laden flow. In the present publication the model is extended for application to a decaying suspension. Also a comparison is given between predictions made with the model and experimental data (own data and data reported in the literature) on a decaying turbulent flow with particles in a water tunnel or in a wind tunnel. For most of the experiments a prediction with reasonable accuracy and an interpretation is possible by means of the model. | |

36. | Beretta, Gian Paolo Nonlinear generalization of Schrödinger's equation uniting quantum mechanics and thermodynamics Journal Article International Journal of Thermodynamics, 11 (2), pp. 49-60, 2008. Abstract | BibTeX | Tags: irreversibility, maximal entropy generation, nonequilibrium relaxation, nonunitary quantum dynamics, quantum thermodinamics, second law, steepest-entropy-ascent | Links: @article{Beretta_Schrodinger_2008, title = {Nonlinear generalization of Schrödinger's equation uniting quantum mechanics and thermodynamics}, author = {Gian Paolo Beretta}, doi = {10.5541/ijot.1034000212}, year = {2008}, date = {2008-01-01}, journal = {International Journal of Thermodynamics}, volume = {11}, number = {2}, pages = {49-60}, abstract = {The nonlinear equation of motion that accomplishes a self-consistent unification of quantum mechanics (QM) and thermodynamics conceptually different from the (von Neumann) foundations of quantum statistical mechanics (QSM) and (Jaynes) quantum information theory (QIT), but which reduces to the same mathematics for the thermodynamic equilibrium (TE) states, and contains standard QM in that it reduces to the time-dependent Schrödinger equation for zero entropy states is discussed in full mathematical detail. By restricting the discussion to a strictly isolated system (noninteracting, disentangled and uncorrelated), we show how the theory departs from the conventional QSM/QIT rationalization of the second law of thermodynamics, which instead emerges in QT (quantum thermodynamics) as a theorem of existence and uniqueness of a stable equilibrium state for each set of mean values of the energy and the number of constituent particles. To achieve this, the theory assumes Trρ lnρ B −k for the physical entropy and is designed to implement two fundamental ansatzs: (1) that in addition to the standard QM states described by idempotent density operators (zero entropy), a strictly isolated and uncorrelated system admits also states that must be described by non-idempotent density operators (nonzero entropy); (2) that for such additional states the law of causal evolution is determined by the simultaneous action of a Schrödinger-von Neumann-type Hamiltonian generator and a nonlinear dissipative generator which conserves the mean values of the energy and the number of constituent particles, and in forward time drives the density operator in the 'direction' of steepest entropy ascent (maximal entropy generation). The resulting dynamics is well defined for all non-equilibrium states, no matter how far from TE. Existence and uniqueness of solutions of the Cauchy initial value problem for all density operators implies that the equation of motion can be solved not only in forward time, to describe relaxation towards TE, but also in backward time, to reconstruct the 'ancestral' or primordial lowest entropy state or limit cycle from which the system originates. Zero entropy states as well as a well defined family of non-dissipative states evolve unitarily according to pure Hamiltonian dynamics and can be viewed as unstable limit cycles of the general nonlinear dynamics.}, keywords = {irreversibility, maximal entropy generation, nonequilibrium relaxation, nonunitary quantum dynamics, quantum thermodinamics, second law, steepest-entropy-ascent}, pubstate = {published}, tppubtype = {article} } The nonlinear equation of motion that accomplishes a self-consistent unification of quantum mechanics (QM) and thermodynamics conceptually different from the (von Neumann) foundations of quantum statistical mechanics (QSM) and (Jaynes) quantum information theory (QIT), but which reduces to the same mathematics for the thermodynamic equilibrium (TE) states, and contains standard QM in that it reduces to the time-dependent Schrödinger equation for zero entropy states is discussed in full mathematical detail. By restricting the discussion to a strictly isolated system (noninteracting, disentangled and uncorrelated), we show how the theory departs from the conventional QSM/QIT rationalization of the second law of thermodynamics, which instead emerges in QT (quantum thermodynamics) as a theorem of existence and uniqueness of a stable equilibrium state for each set of mean values of the energy and the number of constituent particles. To achieve this, the theory assumes Trρ lnρ B −k for the physical entropy and is designed to implement two fundamental ansatzs: (1) that in addition to the standard QM states described by idempotent density operators (zero entropy), a strictly isolated and uncorrelated system admits also states that must be described by non-idempotent density operators (nonzero entropy); (2) that for such additional states the law of causal evolution is determined by the simultaneous action of a Schrödinger-von Neumann-type Hamiltonian generator and a nonlinear dissipative generator which conserves the mean values of the energy and the number of constituent particles, and in forward time drives the density operator in the 'direction' of steepest entropy ascent (maximal entropy generation). The resulting dynamics is well defined for all non-equilibrium states, no matter how far from TE. Existence and uniqueness of solutions of the Cauchy initial value problem for all density operators implies that the equation of motion can be solved not only in forward time, to describe relaxation towards TE, but also in backward time, to reconstruct the 'ancestral' or primordial lowest entropy state or limit cycle from which the system originates. Zero entropy states as well as a well defined family of non-dissipative states evolve unitarily according to pure Hamiltonian dynamics and can be viewed as unstable limit cycles of the general nonlinear dynamics. | |

## 2007 |
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35. | Ooms, Gijs; Vuik, Kees; Poesio, Pietro Core-annular flow through a horizontal pipe: Hydrodynamic counterbalancing of buoyancy force on core Journal Article Physics of Fluids, 19 , pp. 092103, 2007. Abstract | BibTeX | Tags: Core-annular flow, hydrodynamic waves, hydrodynamics, lubrification, viscosity | Links: @article{Ooms_Vuik_Poesio_2007, title = {Core-annular flow through a horizontal pipe: Hydrodynamic counterbalancing of buoyancy force on core}, author = {Gijs Ooms and Kees Vuik and Pietro Poesio}, doi = {10.1063/1.2775521}, year = {2007}, date = {2007-09-28}, journal = {Physics of Fluids}, volume = {19}, pages = {092103}, abstract = {A theoretical investigation has been made of core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity liquid annular layer through a horizontal pipe. Special attention is paid to the question of how the buoyancy force on the core, caused by a density difference between the core and the annular layer, is counterbalanced. From earlier studies it is known that at the interface between the annular layer and the core waves are present that move with respect to the pipe wall. In the present study the core is assumed to consist of a solid center surrounded by a high-viscosity liquid layer. Using hydrodynamiclubrication theory (taking into account the flow in the low-viscosity liquid annular layer and in the high-viscosity liquid core layer) the development of the interfacial waves is calculated. They generate pressure variations in the core layer and annular layer that can cause a net force on the core. Steady eccentric core-annular flow is found to be possible.}, keywords = {Core-annular flow, hydrodynamic waves, hydrodynamics, lubrification, viscosity}, pubstate = {published}, tppubtype = {article} } A theoretical investigation has been made of core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity liquid annular layer through a horizontal pipe. Special attention is paid to the question of how the buoyancy force on the core, caused by a density difference between the core and the annular layer, is counterbalanced. From earlier studies it is known that at the interface between the annular layer and the core waves are present that move with respect to the pipe wall. In the present study the core is assumed to consist of a solid center surrounded by a high-viscosity liquid layer. Using hydrodynamiclubrication theory (taking into account the flow in the low-viscosity liquid annular layer and in the high-viscosity liquid core layer) the development of the interfacial waves is calculated. They generate pressure variations in the core layer and annular layer that can cause a net force on the core. Steady eccentric core-annular flow is found to be possible. | |

34. | Poesio, Pietro; Lezzi, Adriano Maria; Beretta, Gian Paolo Evidence of convective heat transfer enhancement induced by spinodal decomposition Journal Article Physical Review E, 75 (6), pp. 066306, 2007. Abstract | BibTeX | Tags: Heat transfer enhancement, Spinodal decomposition | Links: @article{Poesio_Lezzi_2007, title = {Evidence of convective heat transfer enhancement induced by spinodal decomposition}, author = {Pietro Poesio and Adriano Maria Lezzi and Gian Paolo Beretta}, doi = {10.1103/PhysRevE.75.066306}, year = {2007}, date = {2007-06-07}, journal = {Physical Review E}, volume = {75}, number = {6}, pages = {066306}, abstract = {Spinodal decomposition can be driven by either diffusion or self-induced convection; the importance of convection relative to diffusion depends on the Péclet number, defined as the ratio between convective and diffusive mass fluxes. Diffusion is the dominating mechanism of phase segregation when the Péclet number is small—i.e., when viscosity and diffusivity are large—or when the domain characteristic size is small. For low-viscosity mixtures, convection is the dominating process and the segregation is very rapid as it takes a few seconds compared to the hours needed in the case of pure diffusion. In such cases, strong convective motion of the phase segregating domains is generated even in small-size systems and is almost independent of the temperature difference as long as it is below the transition value. We study experimentally the enhancement of heat transfer in a 1−mm-thick cell. A water-acetonitrile-toulene mixture is quenched into a two-phase region so as to induce convection-driven spinodal decomposition. The heat transfer rate is measured and compared to that obtained in the absence of convective motion. A substantial reduction in the cooling time obtains in the case of spinodal decomposition. The heat transfer enhancement induced by this self-induced, disordered but effectively convective effect may be exploited in the cooling or heating of small-scale systems whereby forced convection cannot be achieved because of the small sizes involved. A scaling analysis of the data based on the diffuse interface H model for a symmetric mixture near the equilibrium point yields very encouraging agreement and insights.}, keywords = {Heat transfer enhancement, Spinodal decomposition}, pubstate = {published}, tppubtype = {article} } Spinodal decomposition can be driven by either diffusion or self-induced convection; the importance of convection relative to diffusion depends on the Péclet number, defined as the ratio between convective and diffusive mass fluxes. Diffusion is the dominating mechanism of phase segregation when the Péclet number is small—i.e., when viscosity and diffusivity are large—or when the domain characteristic size is small. For low-viscosity mixtures, convection is the dominating process and the segregation is very rapid as it takes a few seconds compared to the hours needed in the case of pure diffusion. In such cases, strong convective motion of the phase segregating domains is generated even in small-size systems and is almost independent of the temperature difference as long as it is below the transition value. We study experimentally the enhancement of heat transfer in a 1−mm-thick cell. A water-acetonitrile-toulene mixture is quenched into a two-phase region so as to induce convection-driven spinodal decomposition. The heat transfer rate is measured and compared to that obtained in the absence of convective motion. A substantial reduction in the cooling time obtains in the case of spinodal decomposition. The heat transfer enhancement induced by this self-induced, disordered but effectively convective effect may be exploited in the cooling or heating of small-scale systems whereby forced convection cannot be achieved because of the small sizes involved. A scaling analysis of the data based on the diffuse interface H model for a symmetric mixture near the equilibrium point yields very encouraging agreement and insights. | |

33. | Beretta, Gian Paolo Well-behaved nonlinear evolution equation for steepest-entropy-ascent dissipative quantum dynamics Journal Article International Journal of Quantum Information, 5 (01-02), pp. 249, 2007. Abstract | BibTeX | Tags: entropy, irreversibility, Nonlinear quantum dynamics, quantum thermodinamics | Links: @article{Beretta_quantum_2007, title = {Well-behaved nonlinear evolution equation for steepest-entropy-ascent dissipative quantum dynamics}, author = {Gian Paolo Beretta}, doi = {10.1142/S0219749907002700}, year = {2007}, date = {2007-04-01}, journal = {International Journal of Quantum Information}, volume = {5}, number = {01-02}, pages = {249}, abstract = {In this paper, we outline the main features of the nonlinear quantum evolution equation proposed by the present author. Such an equation may be used as a model of reduced subsystem dynamics to complement various historical and contemporary efforts to extend linear Markovian theories of dissipative phenomena and relaxation based on master equations, Lindblad and Langevin equations, to the nonlinear and far nonequilibrium domain. It may also be used as the fundamental dynamical principle in theories that attempt to unite mechanics and thermodynamics, such as the Hatsopoulos–Gyftopoulos unified theory which motivated the original development of this well-behaved general nonlinear equation for the evolution of the density operator capable of generating irreversible deterministic relaxation to thermodynamic equilibrium from any far nonequilibrium state even for an isolated system.}, keywords = {entropy, irreversibility, Nonlinear quantum dynamics, quantum thermodinamics}, pubstate = {published}, tppubtype = {article} } In this paper, we outline the main features of the nonlinear quantum evolution equation proposed by the present author. Such an equation may be used as a model of reduced subsystem dynamics to complement various historical and contemporary efforts to extend linear Markovian theories of dissipative phenomena and relaxation based on master equations, Lindblad and Langevin equations, to the nonlinear and far nonequilibrium domain. It may also be used as the fundamental dynamical principle in theories that attempt to unite mechanics and thermodynamics, such as the Hatsopoulos–Gyftopoulos unified theory which motivated the original development of this well-behaved general nonlinear equation for the evolution of the density operator capable of generating irreversible deterministic relaxation to thermodynamic equilibrium from any far nonequilibrium state even for an isolated system. | |

32. | Poesio, Pietro; Ooms, Gijs Removal of particle bridges from a porous material by ultrasonic irradiation Journal Article Transport in Porous Media, 66 (3), pp. 235-257, 2007. BibTeX | Tags: fluid flow with particles, lattice-Boltzmann method, permeability reduction, porous material, ultrasonic cleaning | Links: @article{Poesio_Ooms_2007, title = {Removal of particle bridges from a porous material by ultrasonic irradiation}, author = {Pietro Poesio and Gijs Ooms}, doi = {10.1007/s11242-006-0016-x}, year = {2007}, date = {2007-02-01}, journal = {Transport in Porous Media}, volume = {66}, number = {3}, pages = {235-257}, keywords = {fluid flow with particles, lattice-Boltzmann method, permeability reduction, porous material, ultrasonic cleaning}, pubstate = {published}, tppubtype = {article} } | |

31. | Beretta, Gian Paolo World energy consumption and resources: an outlook for the rest of the century Journal Article International Journal of Environmental Technology and Management, 7 (1/2), pp. 99-112, 2007. Abstract | BibTeX | Tags: carbon dioxide production, energy reserves, Energy resources, energy scenario, environmental management, global energy, greenhouse gases, Historical data, local energy policy, world energy consumption | Links: @article{Beretta_energy_2007, title = {World energy consumption and resources: an outlook for the rest of the century}, author = {Gian Paolo Beretta}, doi = {10.1504/IJETM.2007.013239}, year = {2007}, date = {2007-01-01}, journal = {International Journal of Environmental Technology and Management}, volume = {7}, number = {1/2}, pages = {99-112}, abstract = {Historical data on world energy consumption are discussed with reference to current data on energy resources and general correlations between per capita energy consumption in different countries and their level of social and economic development. A balanced scenario for the energy needs and primary resources consumption mix of the rest of the century is proposed and compared with proved and presumed primary energy reserves. The corresponding carbon dioxide production scenario is compared with global natural carbon exchanges and inventory. Complexity and actual dimensions of the global energy problem are emphasised, to note that out-of-context local energy policies are hardly effective.}, keywords = {carbon dioxide production, energy reserves, Energy resources, energy scenario, environmental management, global energy, greenhouse gases, Historical data, local energy policy, world energy consumption}, pubstate = {published}, tppubtype = {article} } Historical data on world energy consumption are discussed with reference to current data on energy resources and general correlations between per capita energy consumption in different countries and their level of social and economic development. A balanced scenario for the energy needs and primary resources consumption mix of the rest of the century is proposed and compared with proved and presumed primary energy reserves. The corresponding carbon dioxide production scenario is compared with global natural carbon exchanges and inventory. Complexity and actual dimensions of the global energy problem are emphasised, to note that out-of-context local energy policies are hardly effective. | |

## 2006 |
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30. | Beretta, Gian Paolo The Hatsopoulos-Gyftopoulos resolution of the Schroedinger-Park paradox about the concept of "state" in quantum statistical mechanics Journal Article Modern Physics Letters A, 21 (37), pp. 2799-2811, 2006. Abstract | BibTeX | Tags: conceptual foundations of quantum mechanics, nature of quantum states, Quantum information theory, Quantum statistical mechanics, quantum thermodinamics | Links: @article{Beretta_2_2006, title = {The Hatsopoulos-Gyftopoulos resolution of the Schroedinger-Park paradox about the concept of "state" in quantum statistical mechanics}, author = {Gian Paolo Beretta}, doi = {10.1142/S0217732306021840}, year = {2006}, date = {2006-10-30}, journal = {Modern Physics Letters A}, volume = {21}, number = {37}, pages = {2799-2811}, abstract = {A seldom recognized fundamental difficulty undermines the concept of individual ``state'' in the present formulations of quantum statistical mechanics (and in its quantum information theory interpretation as well). The difficulty is an unavoidable consequence of an almost forgotten corollary proved by E. Schroedinger in 1936 and perused by J.L. Park, Am. J. Phys., Vol. 36, 211 (1968). To resolve it, we must either reject as unsound the concept of state, or else undertake a serious reformulation of quantum theory and the role of statistics. We restate the difficulty and discuss a possible resolution proposed in 1976 by G.N. Hatsopoulos and E.P. Gyftopoulos, Found. Phys., Vol. 6, 15, 127, 439, 561 (1976).}, keywords = {conceptual foundations of quantum mechanics, nature of quantum states, Quantum information theory, Quantum statistical mechanics, quantum thermodinamics}, pubstate = {published}, tppubtype = {article} } A seldom recognized fundamental difficulty undermines the concept of individual ``state'' in the present formulations of quantum statistical mechanics (and in its quantum information theory interpretation as well). The difficulty is an unavoidable consequence of an almost forgotten corollary proved by E. Schroedinger in 1936 and perused by J.L. Park, Am. J. Phys., Vol. 36, 211 (1968). To resolve it, we must either reject as unsound the concept of state, or else undertake a serious reformulation of quantum theory and the role of statistics. We restate the difficulty and discuss a possible resolution proposed in 1976 by G.N. Hatsopoulos and E.P. Gyftopoulos, Found. Phys., Vol. 6, 15, 127, 439, 561 (1976). | |

29. | Beretta, Gian Paolo Steepest-entropy-ascent irreversible relaxation towards thermodynamic equilibrium: the dynamical ansatz that completes the Gyftopoulos-Hatsopoulos unified theory with a general quantal law of causal evolution Journal Article International Journal of Thermodynamics, 9 (3), pp. 117-128, 2006. Abstract | BibTeX | Tags: ancestral or primordial lowest entropy state, existence and uniqueness, Gyftopoulos-Hatsopoulos unified quantum theory of mechanics and thermodynamics, irreversible relaxation towards stable equilibrium, quantal law of causal evolution | Links: @article{Beretta_2006, title = {Steepest-entropy-ascent irreversible relaxation towards thermodynamic equilibrium: the dynamical ansatz that completes the Gyftopoulos-Hatsopoulos unified theory with a general quantal law of causal evolution}, author = {Gian Paolo Beretta}, doi = {10.5541/ijot.1034000175}, year = {2006}, date = {2006-07-30}, journal = {International Journal of Thermodynamics}, volume = {9}, number = {3}, pages = {117-128}, abstract = {We overview the main features of the general equation of motion that completes the Gyftopoulos-Hatsopoulos unified theory of mechanics and thermodynamics with a quantal law of causal evolution that entails relaxation towards stable equilibrium for any non-equilibrium state, no matter how far from thermodynamic equilibrium. We illustrate with numerical examples the behavior of the equation of motion by discussing spontaneous energy redistribution within an isolated, closed system composed of non-interacting identical particles with energy levels ei and i = 1, 2,…, N. For this system the time-dependent occupation probabilities pi(t) obey the nonlinear rate equations which include functions of the pi(t)’s that maintain invariant the mean energy and the normalization condition. The entropy is a non-decreasing function of time until the initially nonzero occupation probabilities reach a Boltzmann-like canonical distribution over the occupied energy eigenstates. Initially zero occupation probabilities, instead, remain zero at all times. The solutions of the rate equations are unique and well-defined for arbitrary initial conditions pi(0) and for all times, -∞ pubstate = {published}, tppubtype = {article} } We overview the main features of the general equation of motion that completes the Gyftopoulos-Hatsopoulos unified theory of mechanics and thermodynamics with a quantal law of causal evolution that entails relaxation towards stable equilibrium for any non-equilibrium state, no matter how far from thermodynamic equilibrium. We illustrate with numerical examples the behavior of the equation of motion by discussing spontaneous energy redistribution within an isolated, closed system composed of non-interacting identical particles with energy levels ei and i = 1, 2,…, N. For this system the time-dependent occupation probabilities pi(t) obey the nonlinear rate equations which include functions of the pi(t)’s that maintain invariant the mean energy and the normalization condition. The entropy is a non-decreasing function of time until the initially nonzero occupation probabilities reach a Boltzmann-like canonical distribution over the occupied energy eigenstates. Initially zero occupation probabilities, instead, remain zero at all times. The solutions of the rate equations are unique and well-defined for arbitrary initial conditions pi(0) and for all times, -∞<t<+∞. Existence and uniqueness both forward and backward in time allows the reconstruction of the ancestral or primordial lowest entropy state. We also illustrate the structure and main properties of the nonlinear dynamics for a composite system. | |

28. | Poesio, Pietro; Cominardi,; Lezzi, Adriano Maria; Mauri,; Beretta, Gian Paolo Effects of quenching rate and viscosity on spinodal decomposition Journal Article Physical Review E, 74 (1), pp. 011507, 2006. Abstract | BibTeX | Tags: quenching rate, Spinodal decomposition, viscosity | Links: @article{Poesio_Cominardi_2006, title = {Effects of quenching rate and viscosity on spinodal decomposition}, author = {Pietro Poesio and G. Cominardi and Adriano Maria Lezzi and R. Mauri and Gian Paolo Beretta}, doi = {10.1103/PhysRevE.74.011507}, year = {2006}, date = {2006-07-25}, journal = {Physical Review E}, volume = {74}, number = {1}, pages = {011507}, abstract = {Spinodal decomposition of deeply quenched mixtures is studied experimentally, with particular emphasis on the domain growth rate during the late stage of coarsening. We provide some experimental evidence that at high Péclet number, the process is isotropic and the domain growth is linear in time, even at finite quenching rates. In fact, the quenching rate appears to influence the magnitude of the growth rate, but not its scaling law. In the second part of the work we analyze the effect of viscosity on the growth rate. As predicted by the diffuse interface model, we do not find any effect of viscosity on the growth rate of the nucleating drops, although, as expected, the viscosity of the continuous phase does influence the settling speed and thus the total separation time.}, keywords = {quenching rate, Spinodal decomposition, viscosity}, pubstate = {published}, tppubtype = {article} } Spinodal decomposition of deeply quenched mixtures is studied experimentally, with particular emphasis on the domain growth rate during the late stage of coarsening. We provide some experimental evidence that at high Péclet number, the process is isotropic and the domain growth is linear in time, even at finite quenching rates. In fact, the quenching rate appears to influence the magnitude of the growth rate, but not its scaling law. In the second part of the work we analyze the effect of viscosity on the growth rate. As predicted by the diffuse interface model, we do not find any effect of viscosity on the growth rate of the nucleating drops, although, as expected, the viscosity of the continuous phase does influence the settling speed and thus the total separation time. | |

27. | Poesio, Pietro; Ooms, Gijs; Cate, Andreas Ten; Hunt, Julian Interaction and collisions between particles in a linear shear flow near a wall at low Reynolds number Journal Article Journal of Fluid Mechanics, 555 , pp. 113-130, 2006. Abstract | BibTeX | Tags: collisions, linear shear flow, low Reynolds number, particles | Links: @article{Poesio_Ooms_2006, title = {Interaction and collisions between particles in a linear shear flow near a wall at low Reynolds number}, author = {Pietro Poesio and Gijs Ooms and Andreas Ten Cate and Julian C. R. Hunt}, doi = {10.1017/S0022112006008780}, year = {2006}, date = {2006-05-11}, journal = {Journal of Fluid Mechanics}, volume = {555}, pages = {113-130}, abstract = {The flow field around pairs of small particles moving and rotating in a shear flow close to a wall at low but finite Reynolds number (Re) is computed as a function of time by means of the lattice-Boltzmann technique. The total force and torque acting on each particle is computed at each time step and the position of the particles is updated. By considering the lift force and the disturbances induced by the particles, the trajectories of the pair of particles are explained as a function of the distances from the wall and the Reynolds number. It is shown that when particles are positioned in a particular form, they collide forming strings. In particular, we are interested in particle-bridge formation in shear flows, and two collided particles (a string) can be considered as a nucleus of a particle bridge.}, keywords = {collisions, linear shear flow, low Reynolds number, particles}, pubstate = {published}, tppubtype = {article} } The flow field around pairs of small particles moving and rotating in a shear flow close to a wall at low but finite Reynolds number (Re) is computed as a function of time by means of the lattice-Boltzmann technique. The total force and torque acting on each particle is computed at each time step and the position of the particles is updated. By considering the lift force and the disturbances induced by the particles, the trajectories of the pair of particles are explained as a function of the distances from the wall and the Reynolds number. It is shown that when particles are positioned in a particular form, they collide forming strings. In particular, we are interested in particle-bridge formation in shear flows, and two collided particles (a string) can be considered as a nucleus of a particle bridge. | |

26. | Beretta, Gian Paolo Nonlinear model dynamics for closed-system, constrained, maximal-entropy-generation relaxation by energy redistribution Journal Article Physical Review E, 73 (2), pp. 026113, 2006. Abstract | BibTeX | Tags: closed-system, energy redistribution, maximal entropy generation, Model dynamics | Links: @article{Beretta_3_2006, title = {Nonlinear model dynamics for closed-system, constrained, maximal-entropy-generation relaxation by energy redistribution}, author = {Gian Paolo Beretta}, doi = {10.1103/PhysRevE.73.026113}, year = {2006}, date = {2006-02-13}, journal = {Physical Review E}, volume = {73}, number = {2}, pages = {026113}, abstract = {We discuss a nonlinear model for relaxation by energy redistribution within an isolated, closed system composed of noninteracting identical particles with energy levels ei with i=1,2,…,N. The time-dependent occupation probabilities pi(t) are assumed to obey the nonlinear rate equations τdpi∕dt=−pilnpi−α(t)pi−β(t)eipi where α(t) and β(t) are functionals of the pi(t)’s that maintain invariant the mean energy E=∑Ni=1eipi(t) and the normalization condition 1=∑Ni=1pi(t). The entropy S(t)=−kB∑Ni=1pi(t)lnpi(t) is a nondecreasing function of time until the initially nonzero occupation probabilities reach a Boltzmann-like canonical distribution over the occupied energy eigenstates. Initially zero occupation probabilities, instead, remain zero at all times. The solutions pi(t) of the rate equations are unique and well defined for arbitrary initial conditions pi(0) and for all times. The existence and uniqueness both forward and backward in time allows the reconstruction of the ancestral or primordial lowest entropy state. By casting the rate equations in terms not of the pi’s but of their positive square roots pi−−√, they unfold from the assumption that time evolution is at all times along the local direction of steepest entropy ascent or, equivalently, of maximal entropy generation. These rate equations have the same mathematical structure and basic features as the nonlinear dynamical equation proposed in a series of papers ending with G. P. Beretta, Found. Phys. 17, 365 (1987) and recently rediscovered by S. Gheorghiu-Svirschevski [Phys. Rev. A 63, 022105 (2001);63, 054102 (2001)]. Numerical results illustrate the features of the dynamics and the differences from the rate equations recently considered for the same problem by M. Lemanska and Z. Jaeger [Physica D 170, 72 (2002)]. We also interpret the functionals kBα(t) and kBβ(t) as nonequilibrium generalizations of the thermodynamic-equilibrium Massieu characteristic function and inverse temperature, respectively.}, keywords = {closed-system, energy redistribution, maximal entropy generation, Model dynamics}, pubstate = {published}, tppubtype = {article} } We discuss a nonlinear model for relaxation by energy redistribution within an isolated, closed system composed of noninteracting identical particles with energy levels ei with i=1,2,…,N. The time-dependent occupation probabilities pi(t) are assumed to obey the nonlinear rate equations τdpi∕dt=−pilnpi−α(t)pi−β(t)eipi where α(t) and β(t) are functionals of the pi(t)’s that maintain invariant the mean energy E=∑Ni=1eipi(t) and the normalization condition 1=∑Ni=1pi(t). The entropy S(t)=−kB∑Ni=1pi(t)lnpi(t) is a nondecreasing function of time until the initially nonzero occupation probabilities reach a Boltzmann-like canonical distribution over the occupied energy eigenstates. Initially zero occupation probabilities, instead, remain zero at all times. The solutions pi(t) of the rate equations are unique and well defined for arbitrary initial conditions pi(0) and for all times. The existence and uniqueness both forward and backward in time allows the reconstruction of the ancestral or primordial lowest entropy state. By casting the rate equations in terms not of the pi’s but of their positive square roots pi−−√, they unfold from the assumption that time evolution is at all times along the local direction of steepest entropy ascent or, equivalently, of maximal entropy generation. These rate equations have the same mathematical structure and basic features as the nonlinear dynamical equation proposed in a series of papers ending with G. P. Beretta, Found. Phys. 17, 365 (1987) and recently rediscovered by S. Gheorghiu-Svirschevski [Phys. Rev. A 63, 022105 (2001);63, 054102 (2001)]. Numerical results illustrate the features of the dynamics and the differences from the rate equations recently considered for the same problem by M. Lemanska and Z. Jaeger [Physica D 170, 72 (2002)]. We also interpret the functionals kBα(t) and kBβ(t) as nonequilibrium generalizations of the thermodynamic-equilibrium Massieu characteristic function and inverse temperature, respectively. | |

## 2005 |
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25. | Ooms, Gijs; Poesio, Pietro Effect of particle inertia and gravity on the turbulence in a suspension Journal Article Physics of Fluids, 17 (12), pp. 125101, 2005. Abstract | BibTeX | Tags: eddies, suspensions, turbulence effects, turbulence simulations, turbulent flows | Links: @article{Ooms_Poesio_2005, title = {Effect of particle inertia and gravity on the turbulence in a suspension}, author = {Gijs Ooms and Pietro Poesio}, doi = {10.1063/1.2139683}, year = {2005}, date = {2005-12-06}, journal = {Physics of Fluids}, volume = {17}, number = {12}, pages = {125101}, abstract = {A theoretical model is presented for the effect of particle inertia and gravity on the turbulence in a homogeneous suspension. It is an extension of the one-fluid model developed by L’vov, Ooms, and Pomyalov [Phys. Rev. E67, 046314 (2003)], in which the effect of gravity was not considered. In the extended model the particles are assumed to settle in the fluid under the influence of gravity due to the fact that their density is larger than the fluid density. The generation of turbulence by the settling particles is described, with special attention being paid to the turbulence intensity and spectra. A comparison is made with direct numerical simulation calculations and experimental data. Also a sensitivity study is carried out to investigate at which conditions the gravity effect becomes important.}, keywords = {eddies, suspensions, turbulence effects, turbulence simulations, turbulent flows}, pubstate = {published}, tppubtype = {article} } A theoretical model is presented for the effect of particle inertia and gravity on the turbulence in a homogeneous suspension. It is an extension of the one-fluid model developed by L’vov, Ooms, and Pomyalov [Phys. Rev. E67, 046314 (2003)], in which the effect of gravity was not considered. In the extended model the particles are assumed to settle in the fluid under the influence of gravity due to the fact that their density is larger than the fluid density. The generation of turbulence by the settling particles is described, with special attention being paid to the turbulence intensity and spectra. A comparison is made with direct numerical simulation calculations and experimental data. Also a sensitivity study is carried out to investigate at which conditions the gravity effect becomes important. | |

24. | Beretta, Gian Paolo Nonlinear extensions of Schroedinger-von Neumann quantum dynamics: a set of necessary conditions for compatibility with thermodynamics Journal Article Modern Physics Letters A, 20 (13), pp. 977-984, 2005. Abstract | BibTeX | Tags: Microscopic erreversibility, Nonlinear quantum dynamics, Spontaneous decoherence | Links: @article{Beretta_2005, title = {Nonlinear extensions of Schroedinger-von Neumann quantum dynamics: a set of necessary conditions for compatibility with thermodynamics}, author = {Gian Paolo Beretta}, doi = {10.1142/S0217732305017263}, year = {2005}, date = {2005-04-30}, journal = {Modern Physics Letters A}, volume = {20}, number = {13}, pages = {977-984}, abstract = {We propose a list of conditions that consistency with thermodynamics imposes on linear and nonlinear generalizations of standard unitary quantum mechanics that assume a set of true quantum states without the restriction ρ2 = ρ even for strictly isolated systems and that are to be considered in experimental tests of the existence of intrinsic (spontaneous) decoherence at the microscopic level. As part of the discussion, we present a general description of nonequilibrium states.}, keywords = {Microscopic erreversibility, Nonlinear quantum dynamics, Spontaneous decoherence}, pubstate = {published}, tppubtype = {article} } We propose a list of conditions that consistency with thermodynamics imposes on linear and nonlinear generalizations of standard unitary quantum mechanics that assume a set of true quantum states without the restriction ρ2 = ρ even for strictly isolated systems and that are to be considered in experimental tests of the existence of intrinsic (spontaneous) decoherence at the microscopic level. As part of the discussion, we present a general description of nonequilibrium states. | |

## 2004 |
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23. | Poesio, Pietro; Ooms, Gijs Formation and ultrasonic removal of fouling particle structures in a natural porous material Journal Article Journal of Petroleum Science and Engineering, 45 (3-4), pp. 159-178, 2004. Abstract | BibTeX | Tags: fouling, particles, porous material, ultrasonic cleaning | Links: @article{Poesio_Ooms_2004, title = {Formation and ultrasonic removal of fouling particle structures in a natural porous material}, author = {Pietro Poesio and Gijs Ooms}, doi = {10.1016/j.petrol.2004.07.008}, year = {2004}, date = {2004-12-15}, journal = {Journal of Petroleum Science and Engineering}, volume = {45}, number = {3-4}, pages = {159-178}, abstract = {Formation and ultrasonic removal of fouling particle structures in a porous material (caused by the flow of a liquid with small through the material) was studied with natural sandstone. Fouling particles were generated inside the sandstone by changing the composition of the liquid from a 2% KCl brine solution to fresh water. The influence of liquid velocity, particle concentration and ratio of particle diameter to pore diameter on the permeability decrease due to the fouling particles is as anticipated from the formation of particle bridges inside the sandstone. The removal of fouling particles by high frequency acoustic waves also was investigated. The influence of fluid velocity, material permeability and acoustic power input on the cleaning efficiency indicates again that fouling is caused by particle bridges inside the sandstone. The understanding of the formation and ultrasonic removal of fouling particle structures in a porous material is of importance for the design of ultrasonic tools for cleaning the near wellbore region of oil reservoirs.}, keywords = {fouling, particles, porous material, ultrasonic cleaning}, pubstate = {published}, tppubtype = {article} } Formation and ultrasonic removal of fouling particle structures in a porous material (caused by the flow of a liquid with small through the material) was studied with natural sandstone. Fouling particles were generated inside the sandstone by changing the composition of the liquid from a 2% KCl brine solution to fresh water. The influence of liquid velocity, particle concentration and ratio of particle diameter to pore diameter on the permeability decrease due to the fouling particles is as anticipated from the formation of particle bridges inside the sandstone. The removal of fouling particles by high frequency acoustic waves also was investigated. The influence of fluid velocity, material permeability and acoustic power input on the cleaning efficiency indicates again that fouling is caused by particle bridges inside the sandstone. The understanding of the formation and ultrasonic removal of fouling particle structures in a porous material is of importance for the design of ultrasonic tools for cleaning the near wellbore region of oil reservoirs. | |

22. | Beretta, Gian Paolo; Gyftopoulos, Elias Thermodynamic derivations of conditions for chemical equilibrium and of Onsager reciprocal relations for chemical reactors Journal Article Journal of Chemical Physics, 121 (6), pp. 2715-2726, 2004. Abstract | BibTeX | Tags: chemical equilibrium state, chemical reactors, Onsager reciprocity | Links: @article{Beretta_2004, title = {Thermodynamic derivations of conditions for chemical equilibrium and of Onsager reciprocal relations for chemical reactors}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos}, doi = {10.1063/1.1756576}, year = {2004}, date = {2004-08-08}, journal = {Journal of Chemical Physics}, volume = {121}, number = {6}, pages = {2715-2726}, abstract = {For an isolated chemical reactor, we derive the conditions for chemical equilibrium in terms of either energy, volume, and amounts of constituents or temperature, pressure, and composition, with special emphasis on what is meant by temperature and chemical potentials as the system proceeds through nonequilibrium states towards stable chemical equilibrium. For nonequilibrium states, we give both analytical expressions and pictorial representations of the assumptions and implications underlying chemical dynamics models. In the vicinity of the chemical equilibrium state, we express the affinities of the chemical reactions, the reaction rates, and the rate of entropy generation as functions of the reaction coordinates and derive Onsager reciprocal relations without recourse to statistical fluctuations, time reversal, and the principle of microscopic reversibility.}, keywords = {chemical equilibrium state, chemical reactors, Onsager reciprocity}, pubstate = {published}, tppubtype = {article} } For an isolated chemical reactor, we derive the conditions for chemical equilibrium in terms of either energy, volume, and amounts of constituents or temperature, pressure, and composition, with special emphasis on what is meant by temperature and chemical potentials as the system proceeds through nonequilibrium states towards stable chemical equilibrium. For nonequilibrium states, we give both analytical expressions and pictorial representations of the assumptions and implications underlying chemical dynamics models. In the vicinity of the chemical equilibrium state, we express the affinities of the chemical reactions, the reaction rates, and the rate of entropy generation as functions of the reaction coordinates and derive Onsager reciprocal relations without recourse to statistical fluctuations, time reversal, and the principle of microscopic reversibility. | |

21. | Poesio, Pietro; Ooms, Gijs; van Dongen, Marinus; Smeulders, David Removal of small particles from a porous material by ultrasonic irradiation Journal Article Transport in Porous Media, 54 (3), pp. 239-364, 2004. Abstract | BibTeX | Tags: colloidal particles, fines, porous media, ultrasound | Links: @article{Poesio_Ooms_2_2004, title = {Removal of small particles from a porous material by ultrasonic irradiation}, author = {Pietro Poesio and Gijs Ooms and Marinus E. H. van Dongen and David M. J. Smeulders}, doi = {10.1023/B:TIPM.0000003677.35458.63}, year = {2004}, date = {2004-01-01}, journal = {Transport in Porous Media}, volume = {54}, number = {3}, pages = {239-364}, abstract = {A study has been made of the removal of small particles from a porous material by means of ultrasonic irradiation. To that purpose a microscopic theoretical model has been developed to calculate the force of a traveling acoustic wave on a spherical particle attached to the wall of a smooth, cylindrical pore inside the porous material. This force was compared with the adhesion force between a small particle and a pore wall. From the comparison between the two forces the conditions were found, at which particles are detached from pore walls and removed from the porous material. The transformation of the results gained from the microscopic model to macroscopic property (permeability) of the porous material was made by means of the Kozeny relation. The aim is to be able to understand and predict qualitatively the influence of relevant parameters on the ultrasonic cleaning process. Predictions made with the theoretical model were compared with data from experiments carried out with ultrasound to remove particles from Berea sandstone. The agreement is reasonable.}, keywords = {colloidal particles, fines, porous media, ultrasound}, pubstate = {published}, tppubtype = {article} } A study has been made of the removal of small particles from a porous material by means of ultrasonic irradiation. To that purpose a microscopic theoretical model has been developed to calculate the force of a traveling acoustic wave on a spherical particle attached to the wall of a smooth, cylindrical pore inside the porous material. This force was compared with the adhesion force between a small particle and a pore wall. From the comparison between the two forces the conditions were found, at which particles are detached from pore walls and removed from the porous material. The transformation of the results gained from the microscopic model to macroscopic property (permeability) of the porous material was made by means of the Kozeny relation. The aim is to be able to understand and predict qualitatively the influence of relevant parameters on the ultrasonic cleaning process. Predictions made with the theoretical model were compared with data from experiments carried out with ultrasound to remove particles from Berea sandstone. The agreement is reasonable. | |

20. | Ooms, Gijs; Poesio, Pietro Stationary core-annular flow through a horizontal pipe Journal Article Physical Review E, 68 (6), pp. 066301, 2004. Abstract | BibTeX | Tags: Core-annular flow, horizontal pipe | Links: @article{Ooms_Poesio_2004, title = {Stationary core-annular flow through a horizontal pipe}, author = {Gijs Ooms and Pietro Poesio}, doi = {10.1103/PhysRevE.68.066301}, year = {2004}, date = {2004-01-01}, journal = {Physical Review E}, volume = {68}, number = {6}, pages = {066301}, abstract = {A theoretical investigation has been made of core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity annular liquid layer through a horizontal pipe. Special attention is paid to the question how the buoyancy force on the core, caused by a possible density difference between the core and the annular layer, is counterbalanced. From earlier studies it is known that at the core surface ripples are present that have the shape of "bamboo" waves or "snake" waves. They generate pressure variations and secondary flows in the annular layer that can cause a net hydrodynamic force on the core. Using hydrodynamic-lubrication theory (assuming the core to be rigid) it has been shown that for snake waves the lubrication force can counterbalance the buoyancy force. For bamboo waves that is not the case.}, keywords = {Core-annular flow, horizontal pipe}, pubstate = {published}, tppubtype = {article} } A theoretical investigation has been made of core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity annular liquid layer through a horizontal pipe. Special attention is paid to the question how the buoyancy force on the core, caused by a possible density difference between the core and the annular layer, is counterbalanced. From earlier studies it is known that at the core surface ripples are present that have the shape of "bamboo" waves or "snake" waves. They generate pressure variations and secondary flows in the annular layer that can cause a net hydrodynamic force on the core. Using hydrodynamic-lubrication theory (assuming the core to be rigid) it has been shown that for snake waves the lubrication force can counterbalance the buoyancy force. For bamboo waves that is not the case. | |

## 2003 |
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19. | Beretta, Gian Paolo; Malfa, Enrico Flow and heat transfer in cavities between rotor and stator disks Journal Article International Journal of Heat and Mass Transfer, 46 (15), pp. 2715-2726, 2003. Abstract | BibTeX | Tags: cavities between rotor and stator disks, flow transfer, heat transfer | Links: @article{Beretta_2003, title = {Flow and heat transfer in cavities between rotor and stator disks}, author = {Gian Paolo Beretta and Enrico Malfa}, doi = {10.1016/S0017-9310(03)00065-6}, year = {2003}, date = {2003-07-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {46}, number = {15}, pages = {2715-2726}, abstract = {The paper discusses the aerodynamic effects in a rotor–stator arrangement where rotor-induced air flow is important in the gap between rotor and housing bases. The rotor is adiabatic whereas the housing surfaces are assumed isothermal. For the case of a closed housing, the empirical correlations available in the literature for the estimate of moment coefficients due to aerodynamic effects under similar geometrical and kinematic conditions are compared with the results of CFD simulations. The numerical results on moment coefficients, mechanical power dissipation, and velocity fields are in satisfactory agreement. In order to evaluate temperature fields and heat fluxes, because no empirical correlations were found for the adiabatic-rotor/isothermal-stator conditions of interest, a semi-empirical model was developed, based on mass and angular momentum balances and the Reynolds analogy. Numerical results and approximate estimates of temperature distribution on the rotor surfaces are in reasonable agreement, also for the case of a housing open to radial flow through the gap.}, keywords = {cavities between rotor and stator disks, flow transfer, heat transfer}, pubstate = {published}, tppubtype = {article} } The paper discusses the aerodynamic effects in a rotor–stator arrangement where rotor-induced air flow is important in the gap between rotor and housing bases. The rotor is adiabatic whereas the housing surfaces are assumed isothermal. For the case of a closed housing, the empirical correlations available in the literature for the estimate of moment coefficients due to aerodynamic effects under similar geometrical and kinematic conditions are compared with the results of CFD simulations. The numerical results on moment coefficients, mechanical power dissipation, and velocity fields are in satisfactory agreement. In order to evaluate temperature fields and heat fluxes, because no empirical correlations were found for the adiabatic-rotor/isothermal-stator conditions of interest, a semi-empirical model was developed, based on mass and angular momentum balances and the Reynolds analogy. Numerical results and approximate estimates of temperature distribution on the rotor surfaces are in reasonable agreement, also for the case of a housing open to radial flow through the gap. | |

## 2002 |
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18. | Poesio, Pietro; Ooms, Gijs; Schraven, Arthur; van der Bas, Fred Theoretical and experimental investigation of acoustic streaming in a porous material Journal Article Physical Review E, 66 (1), pp. 016309, 2002. Abstract | BibTeX | Tags: acoustic streaming, porous material | Links: @article{Poesio_Ooms_2002, title = {Theoretical and experimental investigation of acoustic streaming in a porous material}, author = {Pietro Poesio and Gijs Ooms and Arthur Schraven and Fred van der Bas}, doi = {10.1103/PhysRevE.66.016309}, year = {2002}, date = {2002-08-01}, journal = {Physical Review E}, volume = {66}, number = {1}, pages = {016309}, abstract = {An experimental and theoretical investigation of the influence of high-frequency acoustic waves on the flow of a liquid through a porous material has been made. Particular attention was paid to the phenomenon of acoustic streaming of the liquid in the porous material due to the damping of the acoustic waves. The experiments were performed on Berea sandstone cores. Two acoustic horns were used with frequencies of 20 and 40 kHz, and with maximum power output of 2 and 0.7 kW, respectively. A high external pressure was applied in order to avoid cavitation. A microphone was used to measure the damping of the waves in the porous material and also temperature and pressure measurements in the flowing liquid inside the cores were carried out. To model the acoustic streaming effect Darcy's law was extended with a source term representing the momentum transfer from the acoustic waves to the liquid. The model predictions for the pressure distribution inside the core under acoustic streaming conditions are in reasonable agreement with the experimental data. }, keywords = {acoustic streaming, porous material}, pubstate = {published}, tppubtype = {article} } An experimental and theoretical investigation of the influence of high-frequency acoustic waves on the flow of a liquid through a porous material has been made. Particular attention was paid to the phenomenon of acoustic streaming of the liquid in the porous material due to the damping of the acoustic waves. The experiments were performed on Berea sandstone cores. Two acoustic horns were used with frequencies of 20 and 40 kHz, and with maximum power output of 2 and 0.7 kW, respectively. A high external pressure was applied in order to avoid cavitation. A microphone was used to measure the damping of the waves in the porous material and also temperature and pressure measurements in the flowing liquid inside the cores were carried out. To model the acoustic streaming effect Darcy's law was extended with a source term representing the momentum transfer from the acoustic waves to the liquid. The model predictions for the pressure distribution inside the core under acoustic streaming conditions are in reasonable agreement with the experimental data. | |

17. | Poesio, Pietro; Ooms, Gijs; Barake, Sander; van der Bas, Fred An investigation of the influence of acoustic waves on the liquid flow through a porous material Journal Article The Journal of the Acoustical Society of America, 111 (5), pp. 2019-2025, 2002. Abstract | BibTeX | Tags: acoustic waves, liquid flow, porous material | Links: @article{Poesio_Ooms_2_2002, title = {An investigation of the influence of acoustic waves on the liquid flow through a porous material}, author = {Pietro Poesio and Gijs Ooms and Sander Barake and Fred van der Bas}, doi = {10.1121/1.1466872}, year = {2002}, date = {2002-06-01}, journal = {The Journal of the Acoustical Society of America}, volume = {111}, number = {5}, pages = {2019-2025}, abstract = {An experimental and theoretical investigation has been made of the influence of high-frequency acoustic waves on the flow of a liquid through a porous material. The experiments have been performed on Berea sandstone cores. Two acoustic horns were used with frequencies of 20 and 40 kHz, and with maximum power output of 2 and 0.7 kW, respectively. Also, a temperature measurement of the flowing liquid inside the core was made. A high external pressure was applied in order to avoid cavitation. The acoustic waves were found to produce a significant effect on the pressure gradient at constant liquid flow rate through the core samples. During the application of acoustic waves the pressure gradient inside the core decreases. This effect turned out to be due to the decrease of the liquid viscosity caused by an increase in liquid temperature as a result of the acoustic energy dissipation inside the porous material. Also, a theoretical model has been developed to calculate the dissipation effect on the viscosity and on the pressure gradient. The model predictions are in reasonable agreement with the experimental data. }, keywords = {acoustic waves, liquid flow, porous material}, pubstate = {published}, tppubtype = {article} } An experimental and theoretical investigation has been made of the influence of high-frequency acoustic waves on the flow of a liquid through a porous material. The experiments have been performed on Berea sandstone cores. Two acoustic horns were used with frequencies of 20 and 40 kHz, and with maximum power output of 2 and 0.7 kW, respectively. Also, a temperature measurement of the flowing liquid inside the core was made. A high external pressure was applied in order to avoid cavitation. The acoustic waves were found to produce a significant effect on the pressure gradient at constant liquid flow rate through the core samples. During the application of acoustic waves the pressure gradient inside the core decreases. This effect turned out to be due to the decrease of the liquid viscosity caused by an increase in liquid temperature as a result of the acoustic energy dissipation inside the porous material. Also, a theoretical model has been developed to calculate the dissipation effect on the viscosity and on the pressure gradient. The model predictions are in reasonable agreement with the experimental data. | |

## 2001 |
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16. | Lezzi, Adriano Maria; Beretta, Gian Paolo; Comini,; Faglia,; Galli,; Sberveglieri, Influence of gaseous species transport on the response of solid state gas sensors within enclosures Journal Article Sensors and Actuators B: Chemical, 78 (1-3), pp. 144-150, 2001. Abstract | BibTeX | Tags: Forced convection, Gas sensors, Mass transfer, Measurement chamber | Links: @article{Lezzi_Beretta_2001, title = {Influence of gaseous species transport on the response of solid state gas sensors within enclosures}, author = {Adriano Maria Lezzi and Gian Paolo Beretta and E. Comini and G. Faglia and G. Galli and G. Sberveglieri}, doi = {10.1016/S0925-4005(01)00805-X}, year = {2001}, date = {2001-08-30}, journal = {Sensors and Actuators B: Chemical}, volume = {78}, number = {1-3}, pages = {144-150}, abstract = {The filling of a measurement chamber for gas sensor characterization, with CO diluted in air by the flow-through method is simulated by using a general-purpose CFD code. Numerical data allow to follow the time evolution of CO concentration at any point inside the chamber, thus representing an helpful tool for designing effective test chambers and for interpreting experimental electrical data. In particular, it is shown that CO concentration over the sensor surface increases with time quite slowly, even if the air–CO jet impinges on the device from a short distance. In addition, a comparison of numerical results with experimental data is presented and discussed.}, keywords = {Forced convection, Gas sensors, Mass transfer, Measurement chamber}, pubstate = {published}, tppubtype = {article} } The filling of a measurement chamber for gas sensor characterization, with CO diluted in air by the flow-through method is simulated by using a general-purpose CFD code. Numerical data allow to follow the time evolution of CO concentration at any point inside the chamber, thus representing an helpful tool for designing effective test chambers and for interpreting experimental electrical data. In particular, it is shown that CO concentration over the sensor surface increases with time quite slowly, even if the air–CO jet impinges on the device from a short distance. In addition, a comparison of numerical results with experimental data is presented and discussed. | |

## 1994 |
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15. | Gyftopoulos, Elias; Flik, Markus; Beretta, Gian Paolo What is diffusion? Journal Article Journal of Energy Resources Technology, 116 (2), pp. 136-139, 1994. Abstract | BibTeX | Tags: Diffusion | Links: @article{Gyftopoulos_Flik_1994, title = {What is diffusion?}, author = {Elias P. Gyftopoulos and Markus I. Flik and Gian Paolo Beretta}, doi = {10.1115/1.2906018}, year = {1994}, date = {1994-06-01}, journal = {Journal of Energy Resources Technology}, volume = {116}, number = {2}, pages = {136-139}, abstract = {In earlier publications, heat Q ← is defined as an interaction that is entirely distinguishable from work W → . The energy exchanged Q ← is T Q times the entropy exchanged S ← , where T Q is the almost common temperature of the interacting systems. Here, we define diffusion as another interaction that is entirely distinguishable from both work and heat, and that involves exchanges of energy, entropy, and amount of a constituent. It is an interaction between two systems A and B that pass through stable equilibrium states while their respective parameters remain fixed, and that have almost equal temperatures T A ≈ T B ≈ T D and almost equal total potentials μ A ≈ μ B ≈ μ D of the diffusing constituent. The exchanges of entropy S → , energy E → , and amount of constituent n → out of one system satisfy the relation S → = (E→ −μ D n → )/T D . In the limit of n → = 0, a diffusion interaction becomes heat.}, keywords = {Diffusion}, pubstate = {published}, tppubtype = {article} } In earlier publications, heat Q ← is defined as an interaction that is entirely distinguishable from work W → . The energy exchanged Q ← is T Q times the entropy exchanged S ← , where T Q is the almost common temperature of the interacting systems. Here, we define diffusion as another interaction that is entirely distinguishable from both work and heat, and that involves exchanges of energy, entropy, and amount of a constituent. It is an interaction between two systems A and B that pass through stable equilibrium states while their respective parameters remain fixed, and that have almost equal temperatures T A ≈ T B ≈ T D and almost equal total potentials μ A ≈ μ B ≈ μ D of the diffusing constituent. The exchanges of entropy S → , energy E → , and amount of constituent n → out of one system satisfy the relation S → = (E→ −μ D n → )/T D . In the limit of n → = 0, a diffusion interaction becomes heat. | |

## 1993 |
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14. | Gyftopoulos, Elias; Beretta, Gian Paolo Entropy generation rate in a chemically reacting system Journal Article Journal of Energy Resources Technology, 115 (3), pp. 208-212, 1993. Abstract | BibTeX | Tags: chemically reacting system, entropy, entropy generation rate | Links: @article{Gyftopoulos_Beretta_2_1993, title = {Entropy generation rate in a chemically reacting system}, author = {Elias P. Gyftopoulos and Gian Paolo Beretta}, doi = {10.1115/1.2905995}, year = {1993}, date = {1993-09-01}, journal = {Journal of Energy Resources Technology}, volume = {115}, number = {3}, pages = {208-212}, abstract = {For a nonchemical-equilibrium state of an isolated system A that has r constituents with initial amounts n a = {n1a , n2a , [[ellipsis]], nra } , and that is subject to τ chemical reaction mechanisms, temperature, pressure, and chemical potentials cannot be defined. As time evolves, the values of the amounts of constitutents vary according to the stoichiometric relations ni (t) = nia + Σj=1 τ νi (j) εj (t) , where νi (j) is the stoichiometric coefficient of the i th constituent in the j -reaction mechanism and εj (t) the reaction coordinate of the j th reaction at time t . For such a state, we approximate the values of all the properties at time t with the corresponding properties of the stable equilibrium state of a surrogate system B consisting of the same constituents as A with amounts equal to ni (t) for i = 1, 2, [[ellipsis]], r , but experiencing no chemical reactions. Under this approximation, the rate of entropy generation is given by the expression Ṡ irr = ε̇ · Y , where ε̇ is the row vector of the τ rates of change of the reaction coordinates, ε̇ = { ε̇1 , [[ellipsis]], ε̇τ }, Y the column vector of the τ ratios a j /T off for j = 1, 2, [[ellipsis]], τ, a j = −Σi=1 r νi (j) μ i ,off , that is, the j th affinity of the stable equilibrium state of the surrogate system B , and μ i ,off , and T off are the chemical potential of the i th constituent and the temperature of the stable equilibrium state of the surrogate system. Under the same approximation, by further assuming that ε̇ can be represented as a function of Y only that is, ε̇(Y ) , with ε̇(0) = 0 for chemical equilibrium, we show that ε̇ = L·Y + (higher order terms in Y ), where L is a τ × τ matrix that must be non-negative definite and symmetric, that is, such that the matrix elements Lij satisfy the Onsager reciprocal relations, Lij = Lji . It is noteworthy that, for the first time, the Onsager relations are proven without reference to microscopic reversibility. In our view, if a process is irreversible, microscopic reversibility does not exist.}, keywords = {chemically reacting system, entropy, entropy generation rate}, pubstate = {published}, tppubtype = {article} } For a nonchemical-equilibrium state of an isolated system A that has r constituents with initial amounts n a = {n1a , n2a , [[ellipsis]], nra } , and that is subject to τ chemical reaction mechanisms, temperature, pressure, and chemical potentials cannot be defined. As time evolves, the values of the amounts of constitutents vary according to the stoichiometric relations ni (t) = nia + Σj=1 τ νi (j) εj (t) , where νi (j) is the stoichiometric coefficient of the i th constituent in the j -reaction mechanism and εj (t) the reaction coordinate of the j th reaction at time t . For such a state, we approximate the values of all the properties at time t with the corresponding properties of the stable equilibrium state of a surrogate system B consisting of the same constituents as A with amounts equal to ni (t) for i = 1, 2, [[ellipsis]], r , but experiencing no chemical reactions. Under this approximation, the rate of entropy generation is given by the expression Ṡ irr = ε̇ · Y , where ε̇ is the row vector of the τ rates of change of the reaction coordinates, ε̇ = { ε̇1 , [[ellipsis]], ε̇τ }, Y the column vector of the τ ratios a j /T off for j = 1, 2, [[ellipsis]], τ, a j = −Σi=1 r νi (j) μ i ,off , that is, the j th affinity of the stable equilibrium state of the surrogate system B , and μ i ,off , and T off are the chemical potential of the i th constituent and the temperature of the stable equilibrium state of the surrogate system. Under the same approximation, by further assuming that ε̇ can be represented as a function of Y only that is, ε̇(Y ) , with ε̇(0) = 0 for chemical equilibrium, we show that ε̇ = L·Y + (higher order terms in Y ), where L is a τ × τ matrix that must be non-negative definite and symmetric, that is, such that the matrix elements Lij satisfy the Onsager reciprocal relations, Lij = Lji . It is noteworthy that, for the first time, the Onsager relations are proven without reference to microscopic reversibility. In our view, if a process is irreversible, microscopic reversibility does not exist. | |

13. | Gyftopoulos, Elias; Beretta, Gian Paolo New developments in thermodynamics Journal Article Journal of the Japan Society of Mechanical Engineers, 96 (892), pp. 210-214, 1993. BibTeX | Tags: thermodynamics @article{Gyftopoulos_Beretta_1_1993, title = {New developments in thermodynamics}, author = {Elias P. Gyftopoulos and Gian Paolo Beretta}, year = {1993}, date = {1993-03-01}, journal = {Journal of the Japan Society of Mechanical Engineers}, volume = {96}, number = {892}, pages = {210-214}, keywords = {thermodynamics}, pubstate = {published}, tppubtype = {article} } | |

## 1990 |
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12. | Niro, Alfonso; Beretta, Gian Paolo Boiling regimes in a closed two-phase thermosyphon Journal Article International Journal of Heat and Mass Transfer, 33 (10), pp. 2099-2110, 1990. Abstract | BibTeX | Tags: Boiling regimes, closed two-phase thermosyphon | Links: @article{Niro_Beretta_1990, title = {Boiling regimes in a closed two-phase thermosyphon}, author = {Alfonso Niro and Gian Paolo Beretta}, doi = {10.1016/0017-9310(90)90112-8}, year = {1990}, date = {1990-10-01}, journal = {International Journal of Heat and Mass Transfer}, volume = {33}, number = {10}, pages = {2099-2110}, abstract = {Experimental results and an analytical model on the boiling mechanisms in a closed two-phase thermosyphon are presented in order to define the frontiers between the main boiling regimes and, in particular, the frontier between intermittent boiling and fully-developed boiling. The boiling regimes are classified on the basis of the frequency of bubble nucleation and the ratio of bubble diameter to device diameter. A criterion for the intermittent/developed-boiling frontier is based on the ratio of the bubble-nucleation waiting time and the bubble growth time. From this criterion a correlation between power throughput, working-fluid pressure and nucleation critical superheat are obtained. Experimental data on operating conditions, temperatures, and nucleation frequencies show the same functional dependence as the proposed correlation.}, keywords = {Boiling regimes, closed two-phase thermosyphon}, pubstate = {published}, tppubtype = {article} } Experimental results and an analytical model on the boiling mechanisms in a closed two-phase thermosyphon are presented in order to define the frontiers between the main boiling regimes and, in particular, the frontier between intermittent boiling and fully-developed boiling. The boiling regimes are classified on the basis of the frequency of bubble nucleation and the ratio of bubble diameter to device diameter. A criterion for the intermittent/developed-boiling frontier is based on the ratio of the bubble-nucleation waiting time and the bubble growth time. From this criterion a correlation between power throughput, working-fluid pressure and nucleation critical superheat are obtained. Experimental data on operating conditions, temperatures, and nucleation frequencies show the same functional dependence as the proposed correlation. | |

## 1987 |
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11. | Beretta, Gian Paolo; Niro, Alfonso; Silvestri, Mario Solid slider bearings lubricated by their own melting or sublimation Journal Article Journal of Tribology, 109 (2), pp. 296-300, 1987. Abstract | BibTeX | Tags: lubrification, Solid slider bearings | Links: @article{Beretta_Niro_1987, title = {Solid slider bearings lubricated by their own melting or sublimation}, author = {Gian Paolo Beretta and Alfonso Niro and Mario Silvestri}, doi = {10.1115/1.3261355}, year = {1987}, date = {1987-04-01}, journal = {Journal of Tribology}, volume = {109}, number = {2}, pages = {296-300}, abstract = {We study the steady-state hydrodynamic lubrication of a solid-solid sliding bearing with spontaneous fusion or sublimation of the solid slider substance. Lubrication is sustained by the fluid film produced by fusion or sublimation. Our analysis extends the recent literature on liquid film lubrication of a melting solid slider to the interesting case of gaseous film lubrication of a sublimating solid slider. The results are in the form of analytical expressions showing the explicit influence of every parameter of the problem, together with conditions specifying the range of validity, and conditions guaranteeing that fusion or sublimation develop the necessary supply of lubricant. For substances like water and bismuth that contract upon melting, we extend the results to the interesting range of conditions dominated by the effect of pressure on the melting temperature.}, keywords = {lubrification, Solid slider bearings}, pubstate = {published}, tppubtype = {article} } We study the steady-state hydrodynamic lubrication of a solid-solid sliding bearing with spontaneous fusion or sublimation of the solid slider substance. Lubrication is sustained by the fluid film produced by fusion or sublimation. Our analysis extends the recent literature on liquid film lubrication of a melting solid slider to the interesting case of gaseous film lubrication of a sublimating solid slider. The results are in the form of analytical expressions showing the explicit influence of every parameter of the problem, together with conditions specifying the range of validity, and conditions guaranteeing that fusion or sublimation develop the necessary supply of lubricant. For substances like water and bismuth that contract upon melting, we extend the results to the interesting range of conditions dominated by the effect of pressure on the melting temperature. | |

10. | Beretta, Gian Paolo Quantum thermodynamics of nonequilibrium. Onsager reciprocity and dispersion-dissipation relations Journal Article Foundations of Physics, 17 (4), pp. 365-381, 1987. Abstract | BibTeX | Tags: dispersion-dissipation, nonequilibrium, Onsager reciprocity, quantum thermodinamics | Links: @article{Beretta_1987, title = {Quantum thermodynamics of nonequilibrium. Onsager reciprocity and dispersion-dissipation relations}, author = {Gian Paolo Beretta}, doi = {10.1007/BF00733374}, year = {1987}, date = {1987-04-01}, journal = {Foundations of Physics}, volume = {17}, number = {4}, pages = {365-381}, abstract = {A generalized Onsager reciprocity theorem emerges as an exact consequence of the structure of the nonlinear equation of motion of quantum thermodynamics and is valid for all the dissipative nonequilibrium states, close and far from stable thermodynamic equilibrium, of an isolated system composed of a single constituent of matter with a finite-dimensional Hilbert space. In addition, a dispersion-dissipation theorem results in a precise relation between the generalized dissipative conductivity that describes the mutual interrelation between dissipative rates of a pair of observables and the codispersions of the same observables and the generators of the motion. These results are presented together with a review of quantum thermodynamic postulates and general results.}, keywords = {dispersion-dissipation, nonequilibrium, Onsager reciprocity, quantum thermodinamics}, pubstate = {published}, tppubtype = {article} } A generalized Onsager reciprocity theorem emerges as an exact consequence of the structure of the nonlinear equation of motion of quantum thermodynamics and is valid for all the dissipative nonequilibrium states, close and far from stable thermodynamic equilibrium, of an isolated system composed of a single constituent of matter with a finite-dimensional Hilbert space. In addition, a dispersion-dissipation theorem results in a precise relation between the generalized dissipative conductivity that describes the mutual interrelation between dissipative rates of a pair of observables and the codispersions of the same observables and the generators of the motion. These results are presented together with a review of quantum thermodynamic postulates and general results. | |

9. | Beretta, Gian Paolo Steepest entropy ascent in Quantum Thermodynamics Journal Article Lecture Notes in Physics, 278 , pp. 441-443, 1987. BibTeX | Tags: quantum thermodinamics, steepest-entropy-ascent | Links: @article{Beretta_SEA_1987, title = {Steepest entropy ascent in Quantum Thermodynamics}, author = {Gian Paolo Beretta}, doi = {10.1007/3-540-17894-5_404}, year = {1987}, date = {1987-01-01}, journal = {Lecture Notes in Physics}, volume = {278}, pages = {441-443}, keywords = {quantum thermodinamics, steepest-entropy-ascent}, pubstate = {published}, tppubtype = {article} } | |

## 1986 |
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8. | Beretta, Gian Paolo A theorem on Lyapunov stability for dynamical systems and a conjecture on a property of entropy Journal Article Journal of Mathematical Physics, 27 , pp. 305-308, 1986. Abstract | BibTeX | Tags: dynamical systems, entropy, Lyapunov stability | Links: @article{Beretta_1_1986, title = {A theorem on Lyapunov stability for dynamical systems and a conjecture on a property of entropy}, author = {Gian Paolo Beretta}, doi = {10.1063/1.527390}, year = {1986}, date = {1986-06-01}, journal = {Journal of Mathematical Physics}, volume = {27}, pages = {305-308}, abstract = {For a general dynamical system, it is proved that an equilibrium state belonging to a continuous family of conditionally stable equilibrium states is stable. The result is applied to quantum thermodynamics to clarify in what restricted sense the entropy functional s( ρ)=−k Tr ρ ln ρ can provide a Lyapunov criterion for the stability of thermodynamic equilibrium. A conjecture on a special positive‐definiteness property of −k Tr ρ ln ρ remains to be proved.}, keywords = {dynamical systems, entropy, Lyapunov stability}, pubstate = {published}, tppubtype = {article} } For a general dynamical system, it is proved that an equilibrium state belonging to a continuous family of conditionally stable equilibrium states is stable. The result is applied to quantum thermodynamics to clarify in what restricted sense the entropy functional s( ρ)=−k Tr ρ ln ρ can provide a Lyapunov criterion for the stability of thermodynamic equilibrium. A conjecture on a special positive‐definiteness property of −k Tr ρ ln ρ remains to be proved. | |

7. | Beretta, Gian Paolo General thermodynamic analysis for engine combustion modeling Journal Article SAE paper 850205, SAE Transactions, 2 , pp. 94-104, 1986. Abstract | BibTeX | Tags: Diesel/Compression ignition engines, Simulation and modeling, Spark ignition engines | Links: @article{Beretta_2_1986, title = {General thermodynamic analysis for engine combustion modeling}, author = {Gian Paolo Beretta}, doi = {10.4271/850205}, year = {1986}, date = {1986-01-01}, journal = {SAE paper 850205, SAE Transactions}, volume = {2}, pages = {94-104}, abstract = {The energy and entropy balance equations in an open control volume are treated analytically by a method that can be applied to any level of modeling (zero-dimensional, quasi-dimensional, and multi-dimensional) of any internal combustion engine (homogeneous-charge, stratified-charge, direct-injection, Diesel, adiabatic, …). The method involves no major assumptions and is, therefore, compatible with any detailed model for physical effects such as liquid fuel atomization and vaporization, heat transfer within the combustion chamber and through its walls, mass transfer (convective and diffusive) within the combustion chamber, with crevice regions, with prechambers, and through the inlet and exhaust ports, temperature, composition, and pressure nonuniformities, and so on. The result is in the form of differential equations for the instantaneous mass fraction of burnt gas mixture and for the entropy generated by irreversibility within the chosen control volume, in terms of the pressure and volume histories and appropriately defined mean variables. The choice of control volume may range from the entire combustion chamber (zero-dimensional approach) to a single mesh point in a numerical solution scheme of the differential local balance equations of mass, chemical species, energy and entropy, coupled with some closure scheme to model diffusion, viscosity, heat conduction and chemical kinetics (multi-dimensional approach). Irrespective of the level of detail of the chosen modeling approach, the entropy balance equation provides an interesting and useful, though very seldom exploited, independent relation to check the consistency of any set of additional modeling assumptions or closure scheme with the second law requirement of nonnegativity of the local and global rate of entropy production by irreversibility.}, keywords = {Diesel/Compression ignition engines, Simulation and modeling, Spark ignition engines}, pubstate = {published}, tppubtype = {article} } The energy and entropy balance equations in an open control volume are treated analytically by a method that can be applied to any level of modeling (zero-dimensional, quasi-dimensional, and multi-dimensional) of any internal combustion engine (homogeneous-charge, stratified-charge, direct-injection, Diesel, adiabatic, …). The method involves no major assumptions and is, therefore, compatible with any detailed model for physical effects such as liquid fuel atomization and vaporization, heat transfer within the combustion chamber and through its walls, mass transfer (convective and diffusive) within the combustion chamber, with crevice regions, with prechambers, and through the inlet and exhaust ports, temperature, composition, and pressure nonuniformities, and so on. The result is in the form of differential equations for the instantaneous mass fraction of burnt gas mixture and for the entropy generated by irreversibility within the chosen control volume, in terms of the pressure and volume histories and appropriately defined mean variables. The choice of control volume may range from the entire combustion chamber (zero-dimensional approach) to a single mesh point in a numerical solution scheme of the differential local balance equations of mass, chemical species, energy and entropy, coupled with some closure scheme to model diffusion, viscosity, heat conduction and chemical kinetics (multi-dimensional approach). Irrespective of the level of detail of the chosen modeling approach, the entropy balance equation provides an interesting and useful, though very seldom exploited, independent relation to check the consistency of any set of additional modeling assumptions or closure scheme with the second law requirement of nonnegativity of the local and global rate of entropy production by irreversibility. | |

## 1985 |
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6. | Beretta, Gian Paolo Effect of irreversible atomic relaxation on resonance fluorescence, absorption, and stimulated emission Journal Article International Journal of Theoretical Physics, 24 (12), pp. 1233-1258, 1985. Abstract | BibTeX | Tags: absorption, irreversible atomic relaxation, Quantum physics, resonance fluorescence, stimulated emission | Links: @article{Beretta_1_1985, title = {Effect of irreversible atomic relaxation on resonance fluorescence, absorption, and stimulated emission}, author = {Gian Paolo Beretta}, doi = {10.1007/BF00670336}, year = {1985}, date = {1985-12-01}, journal = {International Journal of Theoretical Physics}, volume = {24}, number = {12}, pages = {1233-1258}, abstract = {Even for a single isolated constituent of matter, a recent generalization of quantum mechanics, called quantum thermodynamics, postulates the existence of new nonmechanical individual states, not contemplated within conventional quantum mechanics, for which the time evolution is governed by a novel nonlinear equation of motion, which entails an irreversible, energy-preserving internal redistribution mechanism of relaxation towards stable equilibrium. For a single two-level atom interacting with the quantum electromagnetic field, we show that such irreversible internal redistribution mechanism entails interesting corrections to the conventional quantum electrodynamic predictions on absorption, resonance fluorescence, and stimulated emission. For a two-level atom driven near resonance by a nearly monochromatic laser beam, we estimate the corrections implied on the spectral distribution of resonance fluorescence and on the absorption and stimulated emission line shape. We submit that our predictions call for further high-resolution studies of atom-field interactions. For example, the value or a lower bound to the value of the only unknown constant of the theory, namely, the internal redistribution time constant, can only be established by a quantitative experimental study.}, keywords = {absorption, irreversible atomic relaxation, Quantum physics, resonance fluorescence, stimulated emission}, pubstate = {published}, tppubtype = {article} } Even for a single isolated constituent of matter, a recent generalization of quantum mechanics, called quantum thermodynamics, postulates the existence of new nonmechanical individual states, not contemplated within conventional quantum mechanics, for which the time evolution is governed by a novel nonlinear equation of motion, which entails an irreversible, energy-preserving internal redistribution mechanism of relaxation towards stable equilibrium. For a single two-level atom interacting with the quantum electromagnetic field, we show that such irreversible internal redistribution mechanism entails interesting corrections to the conventional quantum electrodynamic predictions on absorption, resonance fluorescence, and stimulated emission. For a two-level atom driven near resonance by a nearly monochromatic laser beam, we estimate the corrections implied on the spectral distribution of resonance fluorescence and on the absorption and stimulated emission line shape. We submit that our predictions call for further high-resolution studies of atom-field interactions. For example, the value or a lower bound to the value of the only unknown constant of the theory, namely, the internal redistribution time constant, can only be established by a quantitative experimental study. | |

5. | Beretta, Gian Paolo; Gyftopoulos, Elias; Park, Quantum thermodynamics. A new equation of motion for a general quantum system Journal Article Il Nuovo Cimento B, 87 (1), pp. 77-97, 1985. Abstract | BibTeX | Tags: quantum mechanics, quantum theory, quantum thermodinamics | Links: @article{Beretta_Gyftopoulos_1985, title = {Quantum thermodynamics. A new equation of motion for a general quantum system}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos and J.L. Park}, doi = {10.1007/BF02729244}, year = {1985}, date = {1985-05-01}, journal = {Il Nuovo Cimento B}, volume = {87}, number = {1}, pages = {77-97}, abstract = {A novel nonlinear equation of motion is proposed for a general quantum system consisting of more than one distinguishable elementary constituent of matter. In the domain of idempotent quantummechanical state operators, it is satisfied by all unitary evolutions generated by the Schrödinger equation. But, in the broader domain of nonidempotent state operators not contemplated by conventional quantum mechanics, it generates a generally nonunitary evolution, it keeps the energy invariant and causes the entropy to increase with time until the system reaches a state of equilibrium or a limit cycle.}, keywords = {quantum mechanics, quantum theory, quantum thermodinamics}, pubstate = {published}, tppubtype = {article} } A novel nonlinear equation of motion is proposed for a general quantum system consisting of more than one distinguishable elementary constituent of matter. In the domain of idempotent quantummechanical state operators, it is satisfied by all unitary evolutions generated by the Schrödinger equation. But, in the broader domain of nonidempotent state operators not contemplated by conventional quantum mechanics, it generates a generally nonunitary evolution, it keeps the energy invariant and causes the entropy to increase with time until the system reaches a state of equilibrium or a limit cycle. | |

4. | Beretta, Gian Paolo Entropy and irreversibility for a single isolated two level system: New individual quantum states and new nonlinear equation of motion Journal Article International Journal of Theoretical Physics, 24 (2), pp. 119-134, 1985. Abstract | BibTeX | Tags: entropy, irreversibility, nonlinear equation of motion, quantum states, single isolated two level system | Links: @article{Beretta_2_1985, title = {Entropy and irreversibility for a single isolated two level system: New individual quantum states and new nonlinear equation of motion}, author = {Gian Paolo Beretta}, doi = {10.1007/BF00672647}, year = {1985}, date = {1985-02-01}, journal = {International Journal of Theoretical Physics}, volume = {24}, number = {2}, pages = {119-134}, abstract = {We propose a new nonlinear equation of motion for a single isolated two-level quantum system. The resulting generalized two-level quantum dynamical theory entails a new alternative resolution of the long-standing dilemma on the nature of entropy and irreversibility. Even for a single isolated degree of freedom, in addition to the individual mechanical states for which all the results of conventional quantum mechanics remain valid, our theory implies the existence of new nonmechanical individual quantum states. These states have nonzero individual entropy and, by virtue of a constant-energy, internal redistribution mechanism, relax irreversibly toward stable equilibrium. We discuss the possibility of an experimental verification of these conclusions by means of a high-resolution, essentially single-particle, magnetic-resonance experiment.}, keywords = {entropy, irreversibility, nonlinear equation of motion, quantum states, single isolated two level system}, pubstate = {published}, tppubtype = {article} } We propose a new nonlinear equation of motion for a single isolated two-level quantum system. The resulting generalized two-level quantum dynamical theory entails a new alternative resolution of the long-standing dilemma on the nature of entropy and irreversibility. Even for a single isolated degree of freedom, in addition to the individual mechanical states for which all the results of conventional quantum mechanics remain valid, our theory implies the existence of new nonmechanical individual quantum states. These states have nonzero individual entropy and, by virtue of a constant-energy, internal redistribution mechanism, relax irreversibly toward stable equilibrium. We discuss the possibility of an experimental verification of these conclusions by means of a high-resolution, essentially single-particle, magnetic-resonance experiment. | |

## 1984 |
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3. | Beretta, Gian Paolo; Gyftopoulos, Elias; Park,; Hatsopoulos, George Quantum thermodynamics. A new equation of motion for a single constituent of matter Journal Article Il Nuovo Cimento B, 82 (2), pp. 169-191, 1984. Abstract | BibTeX | Tags: Quantum physics, quantum theory, quantum thermodinamics | Links: @article{Beretta_Gyftopoulos_1984, title = {Quantum thermodynamics. A new equation of motion for a single constituent of matter}, author = {Gian Paolo Beretta and Elias P. Gyftopoulos and J.L. Park and George .N. Hatsopoulos}, doi = {10.1007/BF02732871}, year = {1984}, date = {1984-08-01}, journal = {Il Nuovo Cimento B}, volume = {82}, number = {2}, pages = {169-191}, abstract = {A novel nonlinear equation of motion is proposed for quantum systems consisting of a single elementary constituent of matter. It is satisfied by pure states and by a special class of mixed states evolving unitarily. But, in general, it generates a nonunitary evolution of the state operator. It keeps the energy invariant and causes the entropy to increase with time until the system reaches a state of equilibrium or a limit cycle.}, keywords = {Quantum physics, quantum theory, quantum thermodinamics}, pubstate = {published}, tppubtype = {article} } A novel nonlinear equation of motion is proposed for quantum systems consisting of a single elementary constituent of matter. It is satisfied by pure states and by a special class of mixed states evolving unitarily. But, in general, it generates a nonunitary evolution of the state operator. It keeps the energy invariant and causes the entropy to increase with time until the system reaches a state of equilibrium or a limit cycle. | |

2. | Beretta, Gian Paolo On the relation between classical and quantum‐thermodynamic entropy Journal Article Journal of Mathematical Physics, 25 , pp. 1507-1510, 1984. Abstract | BibTeX | Tags: entropy, quantum thermodinamics | Links: @article{Beretta_1984, title = {On the relation between classical and quantum‐thermodynamic entropy}, author = {Gian Paolo Beretta}, doi = {10.1063/1.526322}, year = {1984}, date = {1984-01-01}, journal = {Journal of Mathematical Physics}, volume = {25}, pages = {1507-1510}, abstract = {We discuss the unresolved problem of proving rigorously that in the classical limit ℏ→0, the quantum‐thermodynamic entropy functional tends to the classical entropy functional. We state rather restrictive conditions that define the general problem of finding a complete classical phase‐space representation of quantum kinematics. Whether the problem admits of solutions remains an unresolved question. We discuss a physically interesting attempt to relate the structure in the classical limit ℏ→0 of the well‐known Blokhintzev, Wigner, and Wehrl phase‐space functions to the spectral expansion of the quantum state operator.}, keywords = {entropy, quantum thermodinamics}, pubstate = {published}, tppubtype = {article} } We discuss the unresolved problem of proving rigorously that in the classical limit ℏ→0, the quantum‐thermodynamic entropy functional tends to the classical entropy functional. We state rather restrictive conditions that define the general problem of finding a complete classical phase‐space representation of quantum kinematics. Whether the problem admits of solutions remains an unresolved question. We discuss a physically interesting attempt to relate the structure in the classical limit ℏ→0 of the well‐known Blokhintzev, Wigner, and Wehrl phase‐space functions to the spectral expansion of the quantum state operator. | |

## 1983 |
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1. | Beretta, Gian Paolo; Rashidi,; Keck, James Turbulent flame propagation and combustion in spark ignition engines Journal Article Combustion and Flame, 52 , pp. 217-245, 1983. Abstract | BibTeX | Tags: Combustion, Spark ignition engines, Turbulent flame | Links: @article{Beretta_Rashidi_Keck_1983, title = {Turbulent flame propagation and combustion in spark ignition engines}, author = {Gian Paolo Beretta and M. Rashidi and James C. Keck}, doi = {10.1016/0010-2180(83)90135-9}, year = {1983}, date = {1983-06-30}, journal = {Combustion and Flame}, volume = {52}, pages = {217-245}, abstract = {Pressure measurements synchronized with high-speed motion picture records of flame propagation have been made in a transparent piston engine. The data show that the initial expansion speed of the flame front is close to that of a laminar flame. As the flame expands, its speed rapidly accelerates to a quasi-steady value comparable with that of the turbulent velocity fluctuations in the unburned gas. During the quasi-steady propagation phase, a significant fraction of the gas behind the visible front is unburned. Final burnout of the charge may be approximated by an exponential decay in time. The data have been analyzed in a model independent way to obtain a set of empirical equations for calculating mass burning rates in spark ignition engines. The burning equations contain three parameters: the laminar burning speed sl, a characteristic speed uT, and a characteristic length lT. The laminar burning speed is known from laboratory measurements. Tentative correlations relating uT and lT to engine geometry and operating variables have been derived from the engine data.}, keywords = {Combustion, Spark ignition engines, Turbulent flame}, pubstate = {published}, tppubtype = {article} } Pressure measurements synchronized with high-speed motion picture records of flame propagation have been made in a transparent piston engine. The data show that the initial expansion speed of the flame front is close to that of a laminar flame. As the flame expands, its speed rapidly accelerates to a quasi-steady value comparable with that of the turbulent velocity fluctuations in the unburned gas. During the quasi-steady propagation phase, a significant fraction of the gas behind the visible front is unburned. Final burnout of the charge may be approximated by an exponential decay in time. The data have been analyzed in a model independent way to obtain a set of empirical equations for calculating mass burning rates in spark ignition engines. The burning equations contain three parameters: the laminar burning speed sl, a characteristic speed uT, and a characteristic length lT. The laminar burning speed is known from laboratory measurements. Tentative correlations relating uT and lT to engine geometry and operating variables have been derived from the engine data. |

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