HIGH RAYLEIGH NUMBER, TRANSIENT NATURAL CONVECTION IN TALL ENCLOSURES FILLED WITH FLUID SATURATED POROUS MEDIA

摘要

Transient natural convective flow and heat transfer in differentially heated tall enclosures filled with fluid saturated porous media is investigated numerically by considering non-Darcy effects. A second order numerical scheme is used to solve the governing time dependent two-dimensional equations. The effect of the Rayleigh number, Ra, and the Darcy number, Da, on the flow evolution, the boundary layer development and the rate of heat transfer are studied. The modified Prandtl number, Pr{sub}m and the inertial parameter, Λ, are set to unity. The results are presented for aspect ratios of 4, 8 and 16. As it is expected, compared to the enclosures of aspect ratio of unity, the flow in tall enclosures results in a more conductive heat transfer and faster evolution. For high values of modified Rayleigh number (Ra{sub}m≥1000), Darcy flow exist at the top and bottom of the enclosure while non-Darcy flow exist in the rest of the enclosure. This is due to the fact that the advection mechanism dominates the flow at the core of the enclosure, while the diffusion mechanism dominates the flow at the top and bottom of the enclosure.