OSCILLATORY DOUBLE-DIFFUSIVE CONVECTION WITH DIFFERENT BUOYANCY RATIOS IN A POROUS ENCLOSURE
The transient behaviors of oscillatory double diffusive convection of a binary gas mixture in a porous enclosure subject to opposing thermal and compositional buoyancies are investigated numerically by employing the SIMPLE algorithm. Effects of two important parameters, the solutal-to-thermal buoyancy ratio N and the solid-to-fluid heat capacity ratio σ, on the heat and mass transfer characteristics are studied. Steady oscillations occur for σ = 0.9 and N = 0.85∼1.00, and σ = 1.0 and N = 0.75∼0.95 as a result of the interaction between thermal and solutal buoyancy forces. For N < 0.75, the solutal buoyancy force is too small, and the flow oscillates initially and reaches the steady state after the transient period. For N > 1.0, the flow is dominated by the solutal effect, and always circulates in the counter-clockwise direction. Therefore no oscillation occurs. For fixed σ, the frequency of oscillation decreases as N is increased due to reduced net buoyancy force. Time-averaged Nu and Sh also decrease as N is increased as a result of reduced convection effects.