Natural convection in a confined saturated porous medium with horizontal temperature and vertical solutal gradients

Double-diffusive natural convection in a horizontal enclosure filled with saturated porous medium is investigated numerically Brinkman extension of Darcy model is adopted in the analysis. The enclosure is heated and cooled along vertical walls and solutal gradient is imposed vertically. The objective of the work is to understand the physics of the flow and to identify the flow regimes for thermal and solutal dominated flows. Since the number of parameters is large, the results are reported for an aspect ratio of two, Prandtl number of 0.71 (air) and Lewis number of 10 (hydrocarbon fuel). Grashof and Darcy numbers may vary between 10(6)-10(8) and 10(-4)-10(-6), respectively. It is found that the flow becomes unstable for finite range of solutal-to-thermal buoyancy ratio and it is possible to obtain different solutions in this region, depending on the initial condition. Funnel-type channelling flow is predicted along the vertical boundaries for thermally driven flow. Also, for thermally driven flow, concentration reversal is possible due to the thermal advection mechanism. Strong stratified fluid may suppress the thermal convection and hear transfer becomes conductive. (C) 2001 Editions scientifiques et medicales Elsevier SAS.