NATURAL-CONVECTION HEAT-TRANSFER FROM A HORIZONTAL WAVY SURFACE IN A POROUS ENCLOSURE

The effect of surface undulations on the natural convection heat trans fer from an isothermal surface in a Darcian fluid-saturated porous enc losure has been numerically analyzed using the finite element method o n a graded nonuniform mesh system. The flow-driving Rayleigh number Ra together with the geometrical parameters of wave amplitude 4 wave pha se phi, and the number of waves N considered in the horizontal dimensi on of the cavity are found to influence the flow and heat transfer pro cess in the enclosure. For Ra around 50 and above, the phenomenon of f low separation and reattachment is noticed on the walls of the enclosu re. A periodic shift in the reattachment point from the bottom wad to the adjacent wads in the clockwise direction, leading to the manifesta tion of cycles of unicellular and bicellular clockwise and countercloc kwise flows, is observed with the phase varying between 0 degrees and 350 degrees. The counterflow in the secondary circulation zone is inte nsified with the increase in the value of Ra. The counterflow on the w avy wad hinders the heat transfer into the system. An increase in eith er wave amplitude or the number of waves considered per unit length de creases the global heat flux into the system. Only marginal changes in global heat flux are noticed with increasing Ra. On the whole, the co mparison of global heat flux results in the wavy wad case with those o f the horizontal flat wad case shows that, in a porous enclosure, the wavy wall reduces the heat transfer into the system.