Effects of variable viscosity on natural convection flow of an optically thick gray gas past a horizontal surface in the presence of internal heat generation

A numerical investigation to discuss the effects of radiation and variable viscosity on heat and mass transfer characteristics of natural convection over a horizontal surface embedded in a saturated porous medium in the presence of internal heat generation is carried out in this study. The working fluid for the investigation is optically thick gray gas. The Dufour and Soret effects are also taken into account. Similarity transformations are employed to obtain nonlinear ordinary differential equations from the governing equations of the present problem. The numerical results for the transformed governing equations are computed by using commercial boundary value problem solver for ordinary differential equations. The effects are discussed by varying the parameters such as radiation, Dufour and Soret numbers, buoyancy ratio, Prandtl number, Schmidt number, and variable viscosity. Presence of internal heat generation enhances the velocity profile and significantly decreases the concentration boundary layer thickness. On increasing fluid radiation, the temperature of the fluid is higher than that of the surface and the concentration boundary layer thickness decreases away from the surface.