The effect of double stratification on boundary-layer flow and heat transfer of nanofluid over a vertical plate

The problem of double stratification on boundary layer flow and heat transfer induced due to a nanofluid over a vertical plate is investigated. The transport equations employed in the analysis include the effect of Brownian motion, thermophoresis, thermal stratification and solutal stratification parameters. The nonlinear governing equations and their associated boundary conditions are initially cast into dimensionless forms by similarity variables. The resulting systems of equations are then solved numerically using Keller-box method. The solution for the temperature and nanoparticle concentration depends on parameters viz, thermal and solutal stratification parameters, Prandtl number Pr, Lewis number Le, Brownian motion Nb, buoyancy ratio parameter Nr and the thermophoresis parameter Nt. Numerical results are obtained for velocity, temperature and concentration distribution as well as the local Nusselt number and Sherwood number. It is found that the local Nusselt number and Sherwood number decrease with an increase in stratification parameters epsilon(1) and epsilon(2). However, the skin friction coefficient f ''(0) increases with an increase in mass stratification parameter epsilon(2) and decreases with an increase in thermal stratification parameter epsilon(1). The obtained results are displayed both graphically tabular form to illustrate the effect of the stratification parameters on the dimensionless velocity, wall temperature and concentration. The numerical results are compared and found to be in good agreement with previous published result on special cases of the problem. (C) 2013 Elsevier Ltd. All rights reserved.