Etude numérique du transfert de chaleur pour un fluide de Bingham dans une cavité carrée en mode de convection naturelle instationnaire

Dans ce travail, nous étudions numériquement le transfert de chaleur en mode de convection naturelle instationnaire d'un fluide de Bingham placé dans une cavité carrée. L'influence de plusieurs paramètres sur le comportement thermique à été analysée dans cette étude. Il s'agit du nombre de Bingham, nombre de Rayleigh et nombre de Prandtl. Le présent code de calcul a été validé après confrontation de nos résultats à ceux de Osman Turan (2010) dans le cas de la convection naturelle d'un fluide de Bingham dans une cavité carrée

Caractérisation de l'écoulement d'un fluide de Bingham dans une cavité à parois mobiles

La présente étude numérique traite du transfert thermique en mode de convection forcée, mixte et naturelle, au sein d'une cavité, à parois mobiles, contenant un fluide non newtonien obéissant au modèle rhéologique de Bingham. L'étude concerne l'influence du rapport de forme, du nombre de Bingham ainsi que celle du nombre de Richardson sur le comportement hydrodynamique et thermique de l'écoulement du fluide considéré dans cet espace confiné

Convection naturelle au sein d'une cavité carrée munie d'une source chauffante placée sur sa paroi inférieure

La convection thermique au sein des espaces confinés est devenue, ces dernière années, un sujet d'investigation d'une grande importance, vue sa présence dans différentes applications industrielles telles que le refroidissement des composantes électroniques, les réacteurs nucléaire ainsi les pertes thermiques dans les collecteurs solaires. La présente étude traite de l'analyse numérique de la convection naturelle laminaire au sein d'une cavité carrée dont les parois latérales (en d'autre terme, verticales) sont maintenues à une température constante (froide) alors que les parois horizontales sont isolées thermiquement, à l'exception d'une fraction occupant 20% à 80% de la surface inférieure de l'enceinte et centrée par rapport à celle-ci, qui est maintenue à une température constante et uniforme, supérieure à celle des parois latérales (chaude) et ce, grâce à une source de chaleur placée en contact de cette paroi. La résolution des équations régissant l'écoulement et le transfert thermique est approchée par la méthode des volumes finis, avec des volumes de contrôle quadrilatéraux et un mallaige uniforme. L'algorithme SIMPLER est adopté pour traiter le couplage vitesse-pression et par conséquent, les champs de vitesse et de température. L'étude se focalise sur l'influence occasionnée par les variations du nombre de Rayleigh et de la longueur de la fraction chauffée, sur la structure de l'écoulement et du transfert thermique au sein de la cavité remplie entièrement d'un fluide newtonien incompressible. Les résultats obtenus montrent, entre autres, que le transfert thermique s'intensifie suite à l'augmentation du nombre de Rayleigh et de la longueur de la fraction chauffée de la aproi inférieure et ce, suite à l'augmentation de la surface d'échange entre cette fraction chauffée et le fluide

About the Oscillatory Flow Phenomenon within 3D Cylindrical Annulus: Critical Buoyancy and Annulus’ Aspect Ratio for Oscillation Stability

The main purpose of our investigation is to providethe impact of some pertinent parameters,asthe thermal buoyancy and the geometryratio,on the oscillatory flow’stability of a Newtonian fluid which occurs within an annulus, found between a cold outer circular cylinder and a hot inner one, to come out at the end with critical conditions that couldpredict this phenomenon intosuch an industrial geometry. To do so, aphysical model is developed using the Lattice-Boltzmann approachside by side with the finite difference one. The validity of the latter is ascertained after comparison between our primary predictionsand various experimental & theoretical ones. By usinganunsteady-state regime, both Isotherms and velocity profiles of ourconvective fluidare widely inspected. Going far with its value, the use of a critical aspect ratio could die-out the impact of any investigated parameter on the oscillatoryflow. Then, only a conductive regime will take control intothe annulus. It is tonote that athree dimensions D3Q19model was adopted based on a cubical Lattice

About the Oscillatory Flow Phenomenon within 3D Cylindrical Annulus: Critical Buoyancy and Annulus’ Aspect Ratio for Oscillation Stability

The main purpose of our investigation is to providethe impact of some pertinent parameters,asthe thermal buoyancy and the geometryratio,on the oscillatory flow’stability of a Newtonian fluid which occurs within an annulus, found between a cold outer circular cylinder and a hot inner one, to come out at the end with critical conditions that couldpredict this phenomenon intosuch an industrial geometry. To do so, aphysical model is developed using the Lattice-Boltzmann approachside by side with the finite difference one. The validity of the latter is ascertained after comparison between our primary predictionsand various experimental & theoretical ones. By usinganunsteady-state regime, both Isotherms and velocity profiles of ourconvective fluidare widely inspected. Going far with its value, the use of a critical aspect ratio could die-out the impact of any investigated parameter on the oscillatoryflow. Then, only a conductive regime will take control intothe annulus. It is tonote that athree dimensions D3Q19model was adopted based on a cubical Lattice

On the validity of a numerical model predicting heat and mass transfer in porous square cavities with a bottom thermal and solute source: case of pollutants spreading and fuel leaks

The present work refers to the study of natural convection into a confined porous medium, driven by cooperating thermal and solutal buoyancy forces. The side walls are maintained at a uniform temperature and concentration, lower than that of a heat and solute source, which located at the center of the bottom wall, the rest of the horizontal walls are kept insulated. The physical model for the momentum conservation equation makes use of the Brinkman extension of the classical Darcy equation, the set of coupled equations is solved using the finite volume method and the SIMPLER algorithm. To account for the effects of the main parameters such the buoyancy ratio, the Lewis and porous thermal Rayleigh numbers, as well as the source length, heat and mass transfer characteristics are widely inspected and then, new powerful correlations are proposed, which predict within ±1% the numerical results. Note that the validity of the used code was ascertained by comparing our results with experimental data and numerical ones already available in the literature

Numerical study of mixed convection heat transfer in a lid-driven cavity filled with a nanofluid

This paper reports a numerical study of mixed convection in a square enclosure, filled with a mixture of water and different types of nanoparticles. The upper and the bottom walls of the cavity are thermally insulated, while the remaining walls are mobile and differentially heated. In order to solve the general coupled equations, a computer code based on the finite volume method is used and it has been validated after a comparison between the present results and those of the literature. To make clear the effects of the governing parameters on the fluid flow and heat transfer inside the square, a wide range of the Richardson number, taken as 0.01 to 100, and the nanoparticles volume fraction, taken from 0 to 10%, is investigated. The phenomenon is analyzed through streamlines and isotherm plots with a special attention to the Nusselt number. The obtained results show that the mean Nusselt number is an increasing function of the decrease Richardson number, and increases with increasing values of the nanoparticles volume fraction, and far from the natural convection mode, higher heat transfer is noted with Ag-water nanofluid. At the end, useful correlations predicting heat transfer rate as a function of the solid volume fraction are proposed for each value of the Richardson number, which predict the numerical results within ±0.02%

Lid-Driven and Inclined Square Cavity Filled With a Nanofluid: Optimum Heat Transfer

This paper reports a numerical study on mixed convection within a square enclosure, filled with a mixture of water and Cu (or Ag) nanoparticles. It is assumed that the temperature difference driving the convection comes from the side moving walls, when both horizontal walls are kept insulated. In order to solve the general coupled equations, a code based on the finite volume method is used and it has been validated after comparison between the present results and those of the literature. To make clear the effect of the main parameters on fluid flow and heat transfer inside the enclosure, a wide range of the Richardson number, taken from 0.01 to 100, the nanoparticles volume fraction (0% to 10%), and the cavity inclination angle (0º to 180º) are investigated. The phenomenon is analyzed through streamlines and isotherm plots, with special attention to the Nusselt number