THERMAL RADIATION AND VARIABLE VISCOSITY EFFECTS ON UNSTEADY MIXED CONVECTION FLOW IN THE STAGNATION REGION ON A VERTICAL SURFACE EMBEDDED IN A POROUS MEDIUM WITH SURFACE HEAT FLUX

I. A. Hassanien (Egypt) and T. H. Al-Arabi (Saudi Arabia)

Received January 20, 2008

Abstract

The unsteady mixed convection boundary layer flow near the region of a stagnation point on a vertical surface embedded in a non-Darcian porous medium with temperature dependent viscosity and thermal radiation is studied. It is assumed that the unsteadiness is caused by the impulsive motion of the free stream velocity and by sudden increase in the surface temperature. Both the buoyancy assisting and buoyancy opposing flow situations are considered. Also, in this study we consider the presence of a solid matrix which exerting first and second resistance parameters. The partial differential equations governing the flow and heat transfer have been solved numerically using an implicate finite difference scheme. The effects of the first and second resistances, viscosity and radiation parameters, Prandtl number and surface heat flux on the surface shear stress and the heat transfer are discussed. It is found the surface shear stress and the heat transfer increase with time and buoyancy parameter. The surface shear stress decreases with Prandtl number but the heat transfer increases.

Keywords and phrases: unsteady flow, mixed convection, porous media, non-similar solution, finite difference.