Numerical study of forced convection heat transfer of Al2O3-Cu/water hybrid nanofluid in a micro-scale backward facing step channel

The present work numerically investigates the laminar forced convection heat transfer of Al2O3-Cu/water hybrid nanofluid over a micro-scale backward facing step (MBFS) channel using finite volume method. The MBFS channel has an expansion ratio (ER)=1.9423 with a step height (S) = 490 µm. The upstream wall and the step wall are thermally insulated while the downstream wall is heated with a constant heat flux (qs”) = 50000 W/m2. The Reynolds numbers considered in this study range from 100 to 389 whereas the nanoparticle volume fraction (φ) = 0-2% has been used. The results indicate that the increase in volume fraction and Reynolds number enhances the Nusselt number. But the skin friction coefficient decreases with the increase in Reynolds number. The changes in skin friction coefficient are insignificant with increasing volume fraction. The use of Al2O3-Cu/water hybrid nanofluid has a profound effect on heat transfer at small volume fractions. In comparison to water, the maximum enhancement in heat transfer of about 24% has been achieved at Reynolds number of 389 and 2% volume fraction. Besides this, the absolute velocity increases with the increment of volume fraction at a particular Reynolds number.