Mixed convection heat transfer in Sisko fluid with viscous dissipation: Effects of assisting and opposing buoyancy

• The buoyancy parameter exerted stronger influence on the local Nusselt number for shear thinning fluids.
• The skin friction coefficient was increased with an increase in the value of material parameter A.
• The local Nusselt number increased for incremented values of the material parameter A.

Steady mixed convection heat transfer in Sisko fluid over a vertically stretching surface is considered when imposed and buoyancy induced flows are in the same and opposite directions. The flow is induced due to a nonlinear stretching sheet with constant temperature distribution. Viscous dissipation effects are also taken into account. The governing partial differential equations under the framework of a Boussinesq approximation are transformed into ordinary differential equations using a suitable transformation. These equations are solved numerically using an implicit finite difference method for the following parameters: buoyancy parameter (− 3.0 ≤ λ ≤ 2.0), power–law index (0.28 ≤ n ≤ 1.9), material parameter of Sisko fluid (0.2 ≤ A ≤ 1.9), and Eckert number (0.2 ≤ Ec ≤ 0.9). In particular, the effects of these dimensionless parameters on the velocity and temperature fields, the skin friction coefficient, and the local Nusselt numbers are displayed graphically. Numerical results are validated by comparison with analytic results as well as previously published results as a special case of the problem.