Saeed Dinarvand - Department of Mechanical Engineering, Islamic Azad University, Central Tehran Branch, Tehran, Iran
Mohammad Yousefi - Department of Mechanical Engineering, Islamic Azad University, Central Tehran Branch, Tehran, Iran
Ali. J Chamkha - Faculty of Engineering, Kuwait College of Science and Technology, Doha, Kuwait‎

The purpose of this study is to present simulation and numerical solutions to the unsteady flow and heat transfer near stagnation point over a stretching/shrinking sheet in porous medium filled with a hybrid nanofluid. Water (base fluid), nanoparticles of titania and copper were considered as a hybrid nanofluid. It is worth mentioning that evaluating the heat transfer enhancement due to the use of hybrid nanofluids has recently become the center of interest for many researchers. The coupled non-linear boundary-layer equations governing the flow and heat transfer are derived and reduced to a set of coupled non-dimensional equations using the appropriate transformations and then solved numerically as a nonlinear boundary value problem by bvp۴c scheme from MATLAB. To validate the modeling of hybrid nanofluid and also numerical procedure, the value of the skin friction and the heat transfer rate for the limited cases of pure water, titania/water and copper/water is obtained and compared with previously reported results that demonstrate an excellent agreement. In the present investigation, the thermal characteristics of hybrid nanofluid are found to be higher in comparison to the base fluid and fluid containing single nanoparticles, respectively. It can be concluded that both skin friction coefficient and local Nusselt number enhance almost linearly with increasing the copper nanoparticle volume fraction (as second nanoparticle). Besides, the porosity and the magnetic effect amplify heat transfer rate, while the unsteadiness parameter has a reducing effect on heat transfer rate in problem conditions.

Porous media, Magnetic, Hybrid nanofluid, Two-dimensional stagnation point, Analytic model of hybridity