Numerical study of double diffusive mixed convection in a backward facing step channel filled with Cu-water nanofluid

Abstract

In this research work numerical results are discussed for thermo-solutal buoyancy driven fluid convection and associated heat and mass transfer in a backward facing step channel filled with Cu-water nanofluid. The conservation equations for fluid momentum, energy and solutal concentration are derived using velocity-vorticity form of Navier-Stokes equations without involving pressure term. Fluid properties that are influenced by the Cu nanoparticles are modified using Maxwell-Garnett model in the governing equations. Galerkin's finite element method is employed to solve the governing equations for the field variables, velocities, vorticity, temperature and solutal concentration. Backward facing step channel with heated bottom wall with higher concentration is considered for the numerical simulations. Computational results have been discussed for the variation of buoyancy ratio (−10 to 10), Prandtl number (1.76 and 6.2) at different volume fractions (0, 0.05, 0.1, 0.2) of the nanoparticles at Re=200 and Ri=0.1 for the nanofluid. Simulation results obtained indicate that the reattachment length at the downstream of the step increases with increase in buoyancy ratio and nanoparticle volume fraction. The average Nusselt number increases by 77% with increase in nanoparticle volume fraction from 0.0 to 0.2 for maximum negative buoyancy ratio −10, whereas the average Sherwood number decreases by 34% with increase in buoyancy ratio from −10 to 10 and nanoparticle volume fraction from 0.0 to 0.2 at Pr=6.2.