An important feature of the natural convectiondriven by combined buoyancy effects is the diversity of the flow regimes that are possiblein the configuration of section 5, the natural convection flows under conFig. 1. The large number of possible flows is due to the sideration may be divided into two limiting classes, (1)relatively large number of dimensionless parameters heat-transfer-driven flows, i.e. flows dominated by thethat govern the phenomenon, namely, the Rayleigh buoyancy effect due to temperature changes, and (2)number t&z,), the Lewis number (Le), the buoyancy mass-transfer-driven flows where the buoyancy effect isratio (N) and the geometric aspect ratio (H/L). The dominated by density changes associated with connumerical solutions obtained in this study were centration variations. In the first series of numericaldesigned to assess the effect of each of these solutions obtained in this study, and summarized indimensionless parameters. In the same sense, the Table 2, we investigated the intluence of Ra, and Le inpurpose of the scale (order-of-mag~tude) analysis heat-transfer-driven flows. In this class of flows thepresented in the next section is to describe these effects buoyancy ratio N is zero: this means that theanalytically and to sort out the flow regimes that can temperature field is coupled to the flow field and notexist in the porous layer. coupled to the concentration field.