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Opposite double diffusion convection in an annular cavity filled with a mixture of air and helium

This paper reports a numerical study of steady state, two-dimensional double diffusive on natural convection in an annular cavity of moderate aspect ratio, filled with a mixture of air and Helium gas (Pr = 0.7, Le = 0.5) . Neumann and Dirichlet boundary conditions for temperature and solute concentration are applied on the two horizontal cylinders. The binary fluid is set in motion under the effect of the competition of opposing buoyancy forces. The equations modeling the problem are discretized using the Finite Difference Method with the ADI scheme. The results are reported for the aspect ratio of the cavity R = 1.4. For a fixed thermal Rayleigh number RaTL=5×103 (based on the gap width), we visualize different flow regimes when the buoyancy ratio varies between N = −12 and N = 0 . These regimes are characterized either by the number of cells, or the type of the main (large) cell or the location of the counter-rotating cells in the annular space. As far as that goes, we have observed strong improvements in heat and mass transfer rates with the appearance of the multicellular regimes.