Double-diffusive flow in enclosures

Numerical calculations are conducted for two-dimensional steady-state double-diffusive flow in enclosures, where both the temperature and solute gradients are imposed horizontally, and the two buoyancy effects can either augment or counteract each other. Important controlling parameters including the thermal and solutal Grashof numbers, Schmidt number, and Prandtl number, are varied and new insights into the solutions of both the augmenting and counteracting modes gained. Even though the relative directions of the two buoyancy mechanisms reverse between the augmenting and counteracting modes, qualitative similarities in convection characteristics emerge. For both modes, with fixed thermal and solutal Grashof numbers, convection strength increases as the ratio between the Schmidt and Prandtl numbers, i.e., the Lewis number, becomes higher. With appropriate combinations of the Grashof number and buoyancy ratio, multiple-cell flow patterns also appear in both modes, where the length scale disparity due to a large Lewis number causes the convection to be largely controlled by the temperature field within the primary convection cell, and by the solute field either in the region across the cell interface or in the secondary cells. Effects of irregular geometry of the enclosure on the transport processes are also assessed.