NATURAL-CONVECTION IN A VERTICAL SLOT FILLED WITH POROUS-MEDIUM

Natural convection in a porous rectangular cavity with isothermal vertical walls at different temperatures has been studied. It is found that for a given Rayleigh number Ra, the convection Nusselt number Nu(c) (or Nu-1), which represents the enhancement of heat transfer by convection, is inversely proportional to the height/width aspect ratio H as the latter increases. This leads to a very simple correlation expressed as Nu(c)H = a(H > H(m)), where constant a and marginal aspect ratio H(m) are determined numerically. It is demonstrated that this new correlation is consistent with the observation that for a given Ra, the effect of the top and bottom adiabatic ends is limited to a fixed length; beyond that, an asymptotical parallel flow, which coincides with the analytical solution for an infinitely long enclosure, prevails around the mid-height of the enclosure. It is suggested that instead of Nu, Nu(c) ( = Nu-1) be used in the correlation of Nu, Ra and H in order to cover results for high H and low Ra.