NATURAL-CONVECTION BELOW A DOWNWARD FACING HEATED HORIZONTAL SURFACE IN A FLUID-SATURATED POROUS-MEDIUM

The nature of natural convection under a downward facing horizontal su rface in a vast fluid-saturated porous medium is numerically studied T he two-dimensional flow is considered to be symmetric about the mid-ve rtical plane under the surface, and numerical calculations are present ed for one half of the domain. The flow and thermal fields demonstrate no boundary layer behavior, and hence similarity and integral analyse s are not possible. A layer of thermally stratified fluid grows under the central region of the surface, which inhibits flow. Convection pic ks up toward the edges of the surface, where the heat transfer rates a re consequently high. The average Nusselt number (based on the total l ength of the surface) is correlated as Nu = 1.142 Ra-0.37 in the range 30 less than or equal to Ra less than or equal to 1000. The structure of the thermal and flow fields under the heated surface in a porous m edium is explained.