Unsteady mixed convection flow of a nanofluid near orthogonal stagnation point on a vertical permeable surface

The unsteady mixed convection stagnation-point flow of a nanofluid toward a vertical surface is investigated numerically. The external velocity impinges normal to the vertical surface, the surface temperature, and the surface volume fraction of nanoparticles are assumed to vary linearly with the distance from the stagnation point. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. A similarity solution is presented, which depends on the Prandtl number Pr, Lewis number Le, Brownian motion number Nb, and thermophoresis number Nt. The governing system of equations is first transformed into a dimensionless form, and then the resulting equations are solved numerically by using a fourth-order Runge-Kutta scheme coupled with a conventional shooting procedure. The features of the flow, heat, and mass transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. The quantitative comparison of skin friction and heat transfer rates with the published results for special cases is shown.