Mixed convection heat transfer and entropy generation analysis of copper-water nanofluid in a vertical channel with non-uniform heating

This paper reports results of a numerical investigation on mixed convection heat transfer and entropy generation for water-copper nanofluid within a vertical channel. The left wall is subjected to a heat flux density of sinusoidal variation, while the right one is cooled at uniform density. The Buongiorno model is employed to describe the nanofluid flow in order to take into account the thermophoresis effect and the Brownian motion. The governing equations are solved numerically using the finite volume method with the SIMPLE algorithm. The effects of pertinent parameters including the Richardson number (Ri), the heat flux ratio (R-q) and the nanoparticles volume fraction (phi(i)) on the flow and thermal fields, as well as the entropy generation are analyzed for both non-uniform and uniform heating. The results show that the heat transfer rate and the various irreversibility modes are increased with the rise of Ri and Rq and the reduction of phi(i) It is also found that a sinusoidal heating is beneficial for the mean Nusselt number but, unfortunately, it is not favorable for the total entropy generation with augmentation rates of up to 7% and 14%, respectively. A map of the flow reversal occurrence is performed and reveals that the latter is strongly affected by the control parameters. In addition, a correlation is proposed to predict the onset of this phenomena with a maximum deviation of 5% compared to the numerical results.