Lattice Boltzmann method for colloidal dispersions with phase change.

Colloidal dispersions are known to undergo phase transition in a number of processes. This often gives rise to formation of structures in a flowing medium. In this paper, we present a model for flow of a colloidal dispersion with phase change. Two distribution functions are used. The colloid is described as a non-ideal fluid capable of phase change, but rather than taking the dispersion medium as the second fluid, a better choice is the dispersion (water plus colloid) which can be considered as an incompressible fluid. This choice allows a standard Lattice Boltzmann (LB) model for incompressible fluids to be used in combination with for the 'free-energy' LB model for the colloid. The coupling between the two fluids is the drag force on the colloid and the dependence of the viscosity of the overall fluid on the particle volume fraction. The problems raised by characteristic times and lengths have been treated. The main application considered is the growth dynamics or domain structuration of protein dispersions during dead-end filtration on a membrane surface

COMBINED CONDUCTIVE-RADIATIVE HEAT TRANSFER ANALYSIS IN COMPLEX GEOMETRY USING THE MONTE CARLO METHOD

Deterministic methods are commonly used to solve the heat balance equation in three-dimensional (3D) geometries. This article presents a preliminary study to the use of a stochastic method for the computation of the temperature in complex 3D geometries where the combined conductive and radiative heat transfers are coupled in the porous solid phase. The Monte Carlo algorithm and its results are validated by a comparison with the results obtained with a conventional finite-volume method

Energy-Conserving Lattice Boltzmann Thermal Model in Two Dimensions

A discrete velocity model is presented for lattice Boltzmann thermal fluid dynamics. This model is implemented and tested in two dimensions with a finite difference scheme. Comparison with analytical solutions shows an excellent agreement even for wide temperature differences. An alternative approximate approach is then presented for traditional lattice transport schemes

Modélisation mésoscopique des écoulements avec changement de phase à partir de l'équation de Boltzmann-Enskog. Introduction des effets thermiques.

In this post-graduate research, kinetic equations of the Boltzmann type were used to model and simulate two-phase flows with phase change. This work was aimed at two different applications where it is important to understand and finely analyze the mechanisms and dynamics of phase change. The first topic is related to the development of two-phase passive cooling devices for micro-electronics. The second application is the aggregation of colloidal particles that results in the formation of deposits on the surface of a membrane during the process of membrane filtration. For the colloid application, a two fluid model is proposed that adapts existing Lattice Boltzmann methods to solve the flow. Finally, in a more exploratory part, an original method is proposed to solve the Boltzmann-Enskog equation, to deal with flows with phase change including thermal effects.Ce travail de thèse concerne la modélisation et la simulation des écoulements diphasiques avec changement de phase par des équations cinétiques de type Boltzmann. Ce travail est motivé par deux applications distinctes pour lesquelles la compréhension et l'analyse fine des mécanismes et des dynamiques de changement de phase sont nécessaires. Le premier thème concerne la mise au point de dispositifs passifs de refroidissement diphasiques pour la micro-électronique. Le seconde thématique concerne la formation de dépôts de filtration résultant de l'agrégation de particules colloïdales à la surface d'une membrane dans des procédés de filtration membranaire. Pour les applications de type colloïdal, un modèle à deux fluides est proposé en adaptant des méthodes Boltzmann-sur-Réseau de la littérature pour la résolution de l'écoulement. Enfin, dans une partie plus exploratoire, un méthode de résolution originale de l'équation de Boltzmann-Enskog est proposée afin de traiter des écoulements avec changement de phase en incluant les effets thermiques

Numerical study of convective flow with condensation of a pure fluid in capillary regime

International audienceA stationary 2-phase flow model with condensation in the capillary regime, based on a separate flow approach was developed. One of the specificities of the model is that it takes into account the coupling between a cylindrical interface (region with a thin film of liquid) and a hemispherical interface (main meniscus at the end of the condensation region). A specific algorithm was developed for numerical resolution to overcome the difficulty related to the presence of a free boundary condition. Analysis of the liquid–vapour interface profiles and the various local parameters allowed us to establish the heat and mass transfer laws for the particular type of regime studied. We analysed the dominant effects of this type of flow, which are characterised by dimensionless numbers Ca (capillary number) and Bo (boiling number), representing the competition between the capillary, viscous and phase-change effects. The effects due to the difference in density between the two phases and to the Reynolds number were also studied. We show that the mean heat transfer coefficients are driven by the profile of the interface. Hence, in certain situations, even when the liquid film becomes thinner on average an unexpected lowering of the efficiency of heat transfer is obtained. These effects are closely related to the coupling between the thin liquid film region and the main meniscus

Modélisation mésoscopique des écoulements avec changement de phase à partir de l'équation de Boltzmann-Enskog (introduction des effets thermiques)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Modélisation et étude numérique instationnaire de la condensation convective en micro-tube

National audienc

Combined conductive-radiative heat transfer analysis in complex geometry using the Monte Carlo method

International audienceDeterministic methods are commonly used to solve the heat balance equation in three-dimensional (3D) geometries.This article presents a preliminary study to the use of a stochastic method for the computation of the temperature in complex 3D geometries where the combined conductive and radiative heat transfers are coupled in the porous solid phase. The Monte Carlo algorithm and its results are validated by a comparison with the results obtained with a conventional finite-volume method