EFFECT OF THERMAL RAYLEIGH AND LEWIS NUMBERS ON DOUBLE-DIFFUSIVE NATURAL-CONVECTION IN A CLOSED ANNULUS

A numerical study for steady laminar double-diffusive natural convecti on within a vertical closed circular annuus is examined with a constan t temperature and mass species (concentration) difference imposed acro ss the vertical walls. The effects of thermal Rayleigh number (5000 le ss-than-or-equal-to Ra(T) less-than-or-equal-to 100,000) and Lewis num ber (1 less-than-or-equal-to Le less-than-or-equal-to 10) are investig ated for buoyancy ratios of -2, -1.2, -1, and 2, representing conditio ns for mass species dominated opposing, transitional, thermal dominate d opposing, and mass species dominated aiding flows, respectively. The relationships between the thermal Rayleigh number and the average Nus selt and Sherwood numbers for -10 less-than-or-equal-to n less-than-or -equal-to 10 have been obtained for a Lewis number of 5. Also, the rel ationship between the Lewis number and the average Nusselt and Sherwoo d numbers for the same buoyancy ratio range have been obtained for a c onstant thermal Rayleigh number of 50,000. The Lewis and thermal Rayle igh numbers are found to influence the buoyancy ratios at which flow t ransition and flow reversal occur.