Effect of thermo-solutal stratification on recirculation flow patterns in a backward-facing step channel flow

This paper presents results on the combined effect of thermo-solutal buoyancy forces on the recirculatory flow behavior in a horizontal channel with backward-facing step and the ensuing impact on heat and mass transfer phenomena. The governing equations for double diffusive mixed convection are represented in velocity-vorticity form of momentum equations, velocity Poisson equations, energy and concentration equations. Galerkin's finite-element method has been employed to solve the governing equations. Recirculatory flow fields with heat and mass transfer are simulated for opposing and aiding thermo-solutal buoyancy forces by assuming suitable boundary conditions for energy and concentration equations. The effect of Richardson number (0.1 <= Ri <= 10) and buoyancy ratio (-10 <= N <= 10) on the recirculation bubble and Nusselt and Sherwood numbers are studied in detail. For Richardson number greater than unity, distinct variations in the gradients of Nusselt number and Sherwood number with buoyancy ratio are observed for flow regimes with opposing and aiding buoyancy forces. Copyright (C) 2009 John Wiley & Sons, Ltd.