Analysis of nanoparticles migration on natural convective heat transfer of nanofluids

Both experimental and numerical studies are unanimous for enhancing Nusselt number for forced convection of nanofluids with slight difference, but there is inconsistency for natural convection heat transfer of nanofluids. In this paper attempt is made to study the effects of nanoparticles migration on the natural convection behavior of nanofluids. For analysis, a mixture model is used by including important phenomena such as Brownian motion and thermophoresis effects. These two mechanisms are taken into account to compute the slip velocities between the base fluid and nanoparticles. The governing equations are solved numerically and good agreements are observed in comparison with experimental measurements. The slip velocities caused the nanoparticles to move and make the nanofluid nonhomogeneous and the decreasing behavior of Nusselt number with addition of nanoparticles size and volume fraction are observed. Also numerical results indicate that single phase assumption the nanofluid for natural convection is not accurate and behavior of flow for natural convection of nanofluids differs from the base fluid. In addition the effects of thermophoresis parameter, volume fraction and nanoparticle diameter on flow and heat transfer behavior are further analyzed. (C) 2012 Elsevier Masson SAS. All rights reserved.