Mixed Convective Flow of a Casson Fluid over a Vertical Stretching Sheet

A coupled nonlinear boundary value problem arising from a mixed convective flow of a non-Newtonian fluid at a vertical stretching sheet with variable thermal conductivity is investigated in this paper. Casson fluid model is used to describe the non-Newtonian fluid behavior. Using a similarity transformation, the governing equations are transformed into a system of coupled, nonlinear ordinary differential equations and the analytical solutions for the velocity and temperature fields are obtained via a semi-analytical algorithm based on the optimal homotopy analysis method. To validate the method, comparisons are made with the available results in the literature for some special cases and the results are found to be in excellent agreement. The characteristics of the velocity and the temperature fields in the boundary layer have been analyzed for several sets of values of the Casson parameter, the Prandtl number, the temperature dependent thermal conductivity parameter, the velocity exponent parameter and the mixed convection parameter. The presented results through graphs and tables reveal substantial effects of the pertinent parameters on the flow and heat transfer characteristics. Furthermore, an error analysis is offered using an exact residual error and average residual error methods.