Variable viscosity effects on free and mixed convection boundary-layer flow from a horizontal surface in a saturated porous medium - variable heat flux

Abstract

In recent years, the study of convective heat transfer from surfaces embedded in porous media has received considerable attention in the literature. The interest for such studies is motivated by several thermal engineering applications, such as geothermal systems, the storage of nuclear wastes, oil extraction, ground water pollution and thermal insulation. The boundary-layer mixed convection flow over horizontal surface with constant or variable wall temperature or heat flux has been studied by many investigators [1-8]. Recently, the flow over an horizontal surface in saturated porous media for the entire regime of forced to free convection has been investigated by Aldoss et al. [9], Chen [10] for Newtonian fluids and by Kumari et al. [11] for non-Newtonian fluids. In all these studies, it was assumed that the thermophysical properties of the fluid are constant. However, it is known that these properties may change with temperature, especially for fluid viscosity. Variable viscosity effects on the stability of flow and temperature fields were considered by Kassoy and Zebib [12], Strans and Schubert [13], Horne and Sullivan [14] and Gary et al. [15]. The effect of variable viscosity for mixed convection flow over a vertical plate with constant wall temperature in saturated porous media has been investigated by Lai and Kulacki [16]. The free or mixed convection flow taking in to account the effect of variable viscosity over a horizontal surface with variable heat flux has not been studied so far.