MHD natural convection and entropy generation in a trapezoidal enclosure using Cu-water nanofluid

The present work investigates the entropy generation and enhancement of heat transfer in natural convection flow and heat transfer using Copper (Cu)-water nanofluid in the presence of a constant magnetic field. The analysis uses a two dimensional trapezoidal enclosure with the left vertical wall and inclined walls kept in a low constant temperature and a heat source with constant heat flux placed on the bottom wall of the enclosure. The governing equations were discretized by the control volume method and solved numerically by SIMPLE algorithm. The computations were carried out for a wide range of the Rayleigh number (10(4) <= Ra <= 10(7)), Hartman number (0 <= Ha <= 100) and solid volume fraction (0 <= phi <= 0.05). The results show that at Ra = 10(4) and 10(5) the enhancement of the Nusselt number due to presence of nanoparticles increases with the Hartman number, but at higher Rayleigh number, a reduction has been observed. In addition it was observed that the entropy generation is decreased when the nanoparticles are present, while the magnetic field generally increases the magnitude of the entropy generation. (C) 2012 Elsevier Ltd. All rights reserved.