doiSerbia

The unsteady flow of a nanofluid in the stagnation point region of a time-dependent rotating sphere

Malvandi Amir (Mechanical Engineering Department, Amirkabir University of Technology, Tehran, Iran + Sun Air Research Institute (SARI), Ferdowsi University of Mashhad, Mashhad, Iran)

This paper deals with the unsteady boundary layer flow and heat transfer of nanofluid over a time-dependent rotating sphere where the free stream velocity varies continuously with time. The boundary layer equations were normalized via similarity variables and solved numerically. Best accuracy of the results has been obtained for regular fluid with previous studies. The nanofluid is treated as a two-component mixture (base fluid+nanoparticles) that incorporates the effects of Brownian diffusion and thermophoresis simultaneously as the two most important mechanisms of slip velocity in laminar flows. Our outcomes indicated that as A and λ increase, surface shear stresses, heat transfer and concentration rates, climb up. Also, Increasing the thermophoresis Nt is found to decrease in the both values of heat transfer and concentration rates. This decrease supresses for higher thermophoresis number. In addition, it was observed that unlike the heat transfer rate, a rise in Brownian motion Nb, leads to an increase in concentration rate.

Keywords: nanofluid, rotating sphere, similarity solution, unsteady stagnation point, thermophoresis