CONVECTIVE HEAT-TRANSFER IN POROUS AND OVERLYING FLUID LAYERS HEATED FROM BELOW

The onset of convection when a porous layer underlying a fluid layer i s heated from below has been numerically investigated. In order to val idate the interface boundary conditions along with the numerical schem e, the present study has focused on the critical Rayleigh number and t he corresponding number of cells. In addition, the effects of the Rayl eigh number, aspect ratio and thickness ratio on supercritical convect ion in the composite layer have been investigated. The results show th at the number of cells at the critical Rayleigh number (Ra-pc) is in g ood agreement with the previous report based on the linear stability t heory. The abrupt change in convective flow patterns accurately verifi es the precipitous drop of Ra-pc with the increasing the depth ratio ( d) and the rapid change of the wave number (a(p)) near d = 0.12. As Ra -p increases, the cell size changes for all depth ratios (d = 1.0, 0.5 , 0.2, 0.1 and 0). In particular, heat transfer rate changes dramatica lly due to the effects of the aspect ratio and the corresponding numbe r of cells when d = 0.1.