Abstract
A numerical analysis of the transient, laminar, combined free and forced convection over an isothermal vertical plate subjected to a step change in temperature and concentration is presented. Density variation due to temperature and concentration differences is described by the Boussinesq approximation. The problem is found to be characterised by five dimensionless groups, namely, a buoyancy ratio parameter, a forced-free convection parameter, a viscous dissipation parameter, and the Prandtl and Schmidt numbers. The coupled nonlinear partial differential equations are solved numerically using a fully implicit finite difference scheme. An iterative procedure along with relaxation is used to solve the sets of nonlinear simultaneous equations. Results are presented for various values of the governing parameters. In the case of free convection alone, a temporal minimum is observed for both the Nusselt and Sherwood numbers due to an overshoot phenomenon in the transient velocity, temperature and concentration profiles. However, the difference between the temporal minimum and the steady state values is less than 4 percent.
