The aim of the present study is investigation of free convection cooling in an L-shape enclosure filled with copper-water nanofluid. The governing equations are solved numerically using finite volume approach. The effects of the volume fraction of the Cu nanoparticles, Rayleigh number and the aspect ratio of the L-shaped enclosure on the heat transfer coefficient, temperature and velocity profiles are studied. The results show that at high Rayleigh numbers, the dominant heat transfer mechanism shifts from conduction to free convection. By increasing Rayleigh number, the numbers of eddies will increase, but the maximum heat transfer coefficient will decrease. For all ranges of Rayleigh number, increasing the volume fraction of the Cu nanoparticles enhances heat transfer coefficient. The simulation results show that inclusion of a number of pins inside the enclosure has a significant effect on increasing the heat transfer coefficient. Also, inclination angle is another important improvement factor for increasing free convection in the enclosures. The numerical results demonstrate that the enclosure with an inclination angle of omega = 225 degrees, has the maximum heat transfer coefficient. (C) 2014 Elsevier Ltd. All rights reserved.