HEAT TRANSFER ENHANCEMENT IN MIXED CONVECTION USING WATER - γAL 2 O 3 NANOFLUID

In the present work, a numerical study of opposing flows in transient mixed convection in a vertical pipe is extended to Newtonian nanofluids. The objective of this study is to highlight the heat transfer enhancement using water – γAl2O3 nanofluid compared to the base-fluid (e.g. water). The initial forced flow is assumed to be laminar, ascending and fully developed. The transient state is then provoked by the sudden application of a positive inlet temperature step at the entry of the pipe. The tube wall is supposed to be very thin and a convective exchange is considered with the ambient air at the external surface. The working out of the problem uses the continuity equation (Poisson equation), the Navier-Stokes equation and the energy equation based on the stream function and the vorticity. It is observed that the recirculation zone in the vicinity of the wall decreases with the increase in the nanoparticle volume fraction. A higher heat transfer rate with the external air is observed for higher volume fractions of metallic oxide particles.