Effect of time-dependent chemical reaction on stagnation point flow and heat transfer over a stretching sheet in a nanofluid

The unsteady two-dimensional boundary layer stagnation-point flow of a nanofluid over a heated stretching sheet is investigated numerically. The unsteadiness in the flow, temperature and nanoparticle concentration fields is caused by the time-dependence of the stretching velocity, the free stream velocity and the surface temperature and concentration. The transport model employed includes the effects of Brownian motion, thermophoresis and time-dependent chemical reaction. The resulting non-linear governing equations with the associated boundary conditions are solved numerically using the shooting technique with the aid of similarity transformation. The velocity, temperature and nanoparticle volume fraction profiles, as well as the local Nusselt and Sherwood numbers, are analyzed due to the effect of the involved parameters of interest, namely the Brownian motion paramter Nb, thermophoresis parameter Nt, unsteadiness parameter S, velocity ratio parameter beta, chemical reaction parameter gamma, Prandtl number Pr and Lewis number Le. It is found that the mass transfer process at the solid-fluid interface is stopped for some values of Le, Nb,. and Nt despite of the continuity of the heat transfer process for the same parameter values.