Heat transfer enhancement for nanofluid flows over a microscale backward-facing step

Abstract

In this paper, we provide a numerical study of laminar flow in a micro-sized backward-facing step channel for water-based nanofluids containing Al2O3 and TiO2 nanoparticles and investigate the impact of the temperature differences between the inlet and the downward wall temperatures. The present work is the first study to introduce a temperature-dependent separation flow model. The velocity increases with increasing concentration of nanoparticles. However, when comparing Al2O3 and TiO2 nanofluids, Al2O3 has a velocity and shear stress higher than TiO2 for 0.04 volume fraction. Increasing the volume fraction of nanofluid led to an increase in the rate of heat transfer from the wall to the fluid, as the thermal properties improved as the volume ratio increased. The performance efficiency index (PEI) decreases as the volume fraction of the particle increases after a certain amount of nanoparticles. The simulation results of the nanofluid separation flow in the recirculation and reattachment shows that the velocity increases as the temperature difference increases, the size of the primary and secondary recirculation regions behind the step is significantly influenced with the temperature difference, a larger temperature difference means a larger recirculation zone.