Augmentation in heat transfer for a hybrid nanofluid flow over a roughened surface

Abstract

Heat transfer characteristics of mixed convective flow of a hybrid nanofluid along a wavy surface are investigated. Dimensionless equations of the problem are solved utilizing finite difference method. Numerical results revealed that for increasing the amplitude-wavelength ratio, magnetic field strength and volume fractions of Cu and Al2O3 nanoparticles, the thermal boundary-layer increases. Skin friction coefficient and local Nusselt number considerably increase owing to the increase of the volume fractions of nanoparticles and magnetic field parameter. Heat transfer for a flat surface is remarkably higher than that for a wavy surface except around the crests of it. Whatever the forced, mixed or free convection regimes, skin friction coefficient and local Nusselt number are almost linearly correlated with the volume fraction of nanoparticles. Moreover, the Cu nanoparticles provide higher heat transfer than the Al2O3 nanoparticles. It is recognized that the local Nusselt number calculated on 5% volume fraction of Cu nanoparticles is higher by 0.5%, 1.0% and 7.7% respectively for forced, mixed and free convection processes, however, when the volume fraction of nanoparticles is 8% the corresponding increments are 0.9%, 1.6% and 13.3%.