Écoulement des particules surfaciques des lits granulaires dans les cylindres rotatifs : une approche originale

La simulation des écoulements polyphasiques est actuellement un enjeu scientifique, industriel et économique, important. L’étude des systèmes gaz-solide fait appel à des modèles qui mettent en œuvre l’influence des particules et les effets des collisions sur le transfert de quantité de mouvement. L’objectif principal de ce travail est d’améliorer la compréhension, via des simulations, des écoulements de matière dans les cylindres rotatifs et de proposer une contribution à la caractérisation de leur hydrodynamique. Les simulations réalisées avec le code de calcul FLUENT ont permis de confirmer la faisabilité de l’approche CFD pour les études hydrodynamiques des systèmes granulaires. La mise en œuvre de l’outil de simulation dans son état actuel a permis de réaliser des études de validation des modèles et de comparer les résultats numériques aux données expérimentales. Pour mener cette validation de façon satisfaisante, on aborde des cas de simulations clés sur des cylindres rotatifs à l’échelle de laboratoire pour lesquels il existe une base de données intéressante et diversifiée. De cette validation émane une nouvelle approche sur la configuration de l’écoulement des particules de surface dans les lits granulaire à l’intérieur des cylindre rotatif ; un événement nouveau et important est mis en évidence : les vecteurs de vitesse des particules ne sont pas toujours parallèles à la surface libre, comme il est fait état dans les travaux antérieurs ; à la limite supérieure de la couche active elles forment un angle avec la surface libre, ce qui représente une situation typique des particules qui sautillent (avance par petits sauts) pour se déplacer

Three-dimensional computation of natural convection in the presence of magnetic field (cubic enclosure)

Buoyancy-driven magneto hydrodynamic flow in a liquid-metal filled cubic enclosure is investigated by three dimensional numerical simulations. The enclosure is heated and cooled along two opposite vertical walls, all other walls being adiabatic. A uniform magnetic field is applied orthogonally to the gravity vector and to the temperature gradient (i.e., parallel to the isothermal walls). The Prandtl number is = 0.019 (characteristic of Galium); the Rayleigh number is made to vary from 103 to 107, the Hartmann number between 30 to 120 and the electrical conductance of the walls between 0 and 1. The Navier–Stokes equations, for the electrical potential, are solved by a finite volume method using the CFD package CFX-4 with some necessary adaptations. Steady-state conditions are assumed. In all cases, a three-dimensional flow with complex secondary motions and a complex current pattern is established. The results show that the dynamic and temperature fields are strongly affected by variations of the magnetic field intensity and the angle of inclination. Numerical simulations are carried out considering different combinations of Grashof and Hartmann numbers to study their effects on the streamlines, the isotherms and the Nusselt number. Wall electrical conductivity enhances damping by changing the distribution of the induced electric current to one which augments the magnitude of the Lorentz force.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Natural convection with volumetric heat generation and external magnetic field in differentially heated enclosure

International audienceThis work presents a numerical study of natural convection in a laterally heated cavity filled with an electrically conductive fluid (Pr=0.0321) in the presence of an external magnetic field and an internal heat source. The finite volume method with the SIMPLER algorithm is used to solve the system of equations governing the magnetohydrodynamics flow. The influence of volumetric heating S-Q on the flow structure and on the heat transfer within the cavity for Gr=10(4), 10(5), and 10(6) was examined. The effects of aspect ratio (A=1, 0.5, and 2), Prandtl number (low Prandtl number fluids), and magnetic field (Ha=0 to 100) were determined in the steady state with internal heat generation. Two orientations of the magnetic field were considered in order to have better control of the flow. The strongest stabilization of the flow field with internal heat generation is found when the magnetic field is oriented horizontally

Study of natural convection in the presence of magnetic field (cylindric enclosure)

Buoyancy-driven magneto hydrodynamic flow in a liquid-metal filled cylindrical enclosure is investigated by numerical simulations, the finite volume method was applied to solve the mass, momentum and energy equations. The numerical result obtained shows the disappearance of the vortex break down under the effect of an axial temperature gradient between the bottom heated and the top cooled of cylinder. In the case of the natural convection with and without magnetic field for fluid with low Prandtl number, the instability appears in the form of regular oscillations for high values of the critical Grashof number, corresponding to the Hartmann numbers. These oscillations are produced by the multicellular mode of the flow. Diagrams of stability show the dependence of the critical Grashof number and critical frequency with the increase of the Hartmann number. we note that, the action of the magnetic field has a stabilizing effect on the flow.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers