Slip effects on unsteady stagnation point flow of a nanofluid over a stretching sheet

Unsteady two-dimensional stagnation point flow of a nanofluid over a stretching sheet is investigated numerically. In contrast to the conventional no-slip condition at the surface, Navier's slip condition has been applied. The behavior of the nanofluid was investigated for three different nanoparticles in the water-base fluid, namely copper, alumina and titania. Employing the similarity variables, the governing partial differential equations including continuity, momentum and energy have been reduced to ordinary ones and solved via Runge-Kutta-Fehlberg scheme. It was shown that a dual solution exists for negative values of the unsteadiness parameter A and, as it increases, the skin friction Cfr grows but the heat transfer rate Nur takes a decreasing trend. The results also indicated that, unlike the stretching parameter epsilon, increasing in the values of the slip parameter lambda. widen the ranges of the unsteadiness parameter A for which the solution exists. Furthermore, it was found that an increase in both epsilon and lambda intensifies the heat transfer rate. (C) 2013 Elsevier B.V. All rights reserved.