Impact of metal oxide nanoparticles on unsteady stagnation point flow of the hybrid base fluid along a flat surface

This paper deals with a detailed investigation of the effects of various metal oxide nanoparticles on unsteady stagnation point flow of a hybrid base fluid impinging on a flat surface. The 'single-phase' nano fluid model,i.e., the Tiwari and Das model, is considered for the study. We consider water and ethylene glycol in 1:1 ratio as the base fluid and four different types of metal oxides, namely, CuO, TiO₂, ZnO and MgO as the nanoparticles.Using similarity transformations, the conservation equations are transformed into self-similar ordinary differential equations. Dual and unique similarity solutions are obtained for certain set of values of parameters. The analysis explores many important findings. Dual self-similar solutions exist up to a certain critical value of the decelerating unsteady parameter and the critical value is independent of the type of metal oxide nanoparticles considered. The strongest surface drag force is observed for the nano fluid with CuO nanoparticles, while the weakest is for the nano fluid with MgO nanoparticles. The heat transfer rate is highest for the nano fluid with CuO nanoparticles and lowest for the nano fluid with TiO₂ nanoparticles. Also, the boundary layer is thickest for the nano fluid with multiprocessing MgO nanoparticles. (author)