AbstractThis article presents a numerical study of natural convection and entropy generation of Cu-water nanofluid within an enclosure with a conductive baffle embedded on bottom hot wall. The governing equations are solved numerically with Finite Volume Method using the SIMPLER algorithm. Effects of Rayleigh number, position of conductive baffle and volume fraction of nanoparticles on the streamlines, isotherms, mean Nusselt number, entropy generation, Bejan number and irreversibility factor have been studied. At Ra=104 the convection heat transfer is very weak and the dominant conduction weakens by displacing the baffle toward the center of the cavity, thus the mean Nusselt number decreases. At higher Rayleigh numbers due to enhanced convection, the improved mean Nusselt number increases by increasing the volume fraction and displacing the baffle toward the center of the cavity. The effect of volume fraction and position of the baffle on entropy generation and Bejan number at Ra=104 is different from Ra=105 and 106. This is due to the effects of addition of nanoparticles on the effective viscosity and conductivity of nanofluid and conduction dominance. It has been shown that assuming a constant irreversibility factor, χ, with change of Ra and φ is not correct.