International Journal

fl tion tube are proposed to calculate the Nusselt number in the fully developed region for horizontal and vertical tubes, for Rayleigh number from 5 105 to 9.6 105, Reynolds number from 350 to 900 and particle volume concentrations up to 4%. Crown Copyright 2010 Published by Elsevier Masson SAS. All rights reserved. itted luids fo Keblinski et al. [6] and Eastman et al. [7] have attributed it to several factors such as the Brownian motion of nanoparticles, the molec-ular level layering of the liquid at the liquid/particle interface, the phonon heat transport inside nanoparticles and the effects due to the nanofluid effective thermal conductivity [1e3,7,8,11e13]. Some studies also provide data for the nanofluid effective viscosity [2,11,12,14]. Wang & Mujumdar [15] presented a review of recent research works on the heat transfer characteristics of nanofluids. Several numerical and experimental works have been carried out to study the hydrodynamic and thermal behaviour of nanofluids in confined flows. For forced convective heat transfer, Pak & Cho [11] studied the heat transfer behaviour in heated tubes and observed that, for a given Reynolds number, the convective heat transfe