WALL EFFECT ON MIXED CONVECTION FROM HORIZONTAL SURFACES WITH A VARIABLE SURFACE HEAT-FLUX

This work investigates analytically the wall effect on the mixed conve ction from a horizontal plate embedded in porous media. Variable surfa ce heat flux is assumed at the plate. The wall effect due to no-slip b oundary condition at the wall is introduced using the Brinkman model. Two sets of transformations are used, one for the forced convection do minating regime (FCDR) and the other one for the natural convection do minating regime (NCDR). The wall effect is found to be characterized b y the boundary parameters L = Da(x)Pe(x)/epsilon in FCDR and by M = Da (x)Ra(x)2/3/epsilon in NCDR. Velocity as well as temperature profiles are calculated at different values of governing parameters. Local Nuss elt number variation for the entire mixed convection regime is also ca lculated and presented. Accurate correlations for local and average Nu sselt number valid for the entire regime of mixed convection and for t he range of boundary-parameter from 0 to 100 are obtained.