JOURNAL OF CENTRAL SOUTH UNIVERSITY

In this study, magneto-hydrodynamics (MHD) mixed convection effects of Al2O3-water nanofluid flow over a backward-facing step were investigated numerically for various electrical conductivity models of nanofluids. A uniform external magnetic field was applied to the flow and strength of magnetic field was varied with different values of dimensionless parameter Hartmann number (Ha=0, 10, 20, 30, 40). Three different electrical conductivity models were used to see the effects of MHD nanofluid flow. Besides, five different inclination angles between 0o90o is used for the external magnetic field. The problem geometry is a backward-facing step which is used in many engineering applications where flow separation and reattachment phenomenon occurs. Mixed type convective heat transfer of backward-facing step was examined with various values of Richardson number (Ri=0.01, 0.1, 1, 10) and four different nanoparticle volume fractions (O=0.01, 0.015, 0.020, 0.025) considering different electrical conductivity models. Finite element method via commercial code COMSOL was used for computations. Results indicate that the addition of nanoparticles enhanced heat transfer significantly. Also increasing magnetic field strength and inclination angle increased heat transfer rate. Effects of different electrical conductivity models were also investigated and it was observed that they have significant effects on the fluid flow and heat transfer characteristics in the presence of magnetic field