This paper analyzes heat transfer and fluid flow of natural convection in a vertical closed chamber filled with Al2O3/water nanofluid that operates under differentially heated walls. The Navier-Stokes and energy equations are solved numerically using the finite element technique with Galerkin's weighted residual simulation. The heat transfer rates are examined for parameters of nanoparticle volume fraction (phi), Prandtl number (Pr) and cavity aspect ratio (AR). Enhanced and mitigated heat transfer effects due to the presence of nanoparticles are identified and highlighted. Based on these insights, the impact of fluid temperature on the heat transfer of nanofluid are determined. Decreasing the Prandtl number results in amplifying the effects of nanoparticles due to increased effective thermal diffusivity. The results highlight the range where the heat transfer uncertainties can be affected by the volume fraction of the nanoparticles. In addition, a correlation is developed graphically for the average Nusselt number as a function of the cavity aspect ratio. (C) 2012 Elsevier Ltd. All rights reserved.