Entropy generation of Cu-water nanofluid mixed convection in a cavity

In this numerical work, mixed convection and entropy generation of Cu-water nanofluid and pure water in a lid-driven square cavity have been studied. Horizontal walls of the cavity are adiabatic and vertical walls have constant temperature but different values. The top wall has been considered as moving from left to right at a constant speed, U-0. Rayleigh numbers of 10(4), 10(5) and 10(6) and Reynolds numbers of 1, 10 and 100 have been considered. The results have shown that addition of nanoparticles to the base fluid affects the entropy generation, flow pattern and thermal behavior especially at higher Rayleigh and low Reynolds numbers. For pure fluid as well as nanofluid, increasing Reynolds number increases the average Nusselt number, linearly. The maximum entropy generation occurs in nanofluid at low Rayleigh number but high Reynolds number. The minimum entropy generation occurs in pure fluid at low Rayleigh and low Reynolds numbers. For the cases studied, at Rayleigh numbers greater than 10(5), most of the entropy generation is due to heat transfer effects, thus the Bejan number converges to a constant value. A proper choice of Reynolds number is important, if enhanced heat transfer and minimum increased entropy generation is expected. (C) 2012 Elsevier Masson SAS. All rights reserved.