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EFFECT OF NON UNIFORM CONDUCTIVITY ON NATURAL CONVECTION ACROSS A HORIZONTAL LAYERED POROUS CAVITY

DOI: 10.1615/ICHMT.2008.CHT.1150
12 pages

Yacine Ould-Amer
Laboratoire des Transports Polyphasiques et Milieux Poreux, Departement de Genie Mecanique, USTHB, B.P. 32, El Alia, Bab Ezzouar 16111, Algeria

Abstract

In the present work, steady natural convection in an enclosure filled with three horizontally layered porous media is studied numerically. Every layer is considered homogeneous, isotropic and saturated with an incompressible fluid. The lateral faces are maintained at different temperatures while the horizontal faces are isolated. In this situation a two dimensional natural convection settles in the porous cavity. The general model including inertial, viscous and parietal effects has been kept. The dimensionless governing parameters include the Darcy number of each layer, the Grashoff number Gr, the Prandtl number Pr and the ratios of thermal conductivity between the porous layers Rc2 and Rc3 with Rc2 = k2/k1 and Rc3= k3/k1. The control volume approach with SIMPLER algorithm was adopted to resolve numerically the physical situation. The results are presented to show the effect of non uniform conductivity on the heat transfer and fluid flow characteristics. The results comprise the streamlines and isotherms patterns and the average Nusselt number. It is found that thermal conductivity ratios between porous layers affect considerably the flow structure and heat transfer. Average Nusselt number increases for conductivity ratios values greater than 1 and decreases for values lesser than 1. The mean Nusselt number improvement reaches 200% in conduction mode and 50% in convection mode when the heat transfer for conductivity ratios unity is being as reference.

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