Conjugate heat transfer of laminar mixed convection of a nanofluid through a horizontal tube with circumferentially non-uniform heating

Laminar mixed convection of a nanofluid consisting of water and Al2O3 in a horizontal tube with heating at the top half surface of a copper tube has been studied numerically. The bottom half of the tube wall is well insulated and can be assumed adiabatic. Heat conduction mechanism is considered through the tube wall. Three dimensional governing equations with using two-phase mixture model have been used to investigate hydrodynamic and thermal behaviour of the nanofluid over wide range of nanoparticle volume fraction. For a given nanoparticle mean diameter the effects of nanoparticle volume fraction on the hydrodynamics and thermal parameters are presented and discussed at different Richardson numbers. It is shown that increasing the nanoparticle concentration significantly augments the heat transfer coefficient while the skin friction coefficient does not considerably affect. (C) 2011 Elsevier Masson SAS. All rights reserved.