Numerical Simulation of Double-Diffusive Natural Convection within a Closed Annulus

Abstract

A numerical study for steady laminar double-diffusive natural convection within a vertical closed annulus is examined with a constant temperature and mass species (concentration) difference imposed across the vertical walls. System parameters are the thermal Rayleigh number, the buoyancy ratio, the Lewis number and the Prandtl number, with the aspect ratio and the curvature ratio as the physical enclosure parameters. The effect of the buoyancy ratio, thermal Rayleigh number and Lewis number was investigated on the flow structure and the average Nusselt and Sherwood numbers. Resulting flow structures were found to fall into three categories: mass species buoyancy force dominated circulation, thermal buoyancy force dominated circulation and transitional flow. It was determined that the solutions in the flow reversal range are not unique, with two or three solutions for the same parameters depending on the original flow conditions. The extent of this flow reversal range is defined by upper and lower critical buoyancy ratios which are influenced by the Lewis and thermal Rayleigh numbers.