MHD mixed convection of nanofluid flov over a backward-facing step

In this study, MHD mixed convection effects of Al2O3-water nanofluid flow over a backward-facing step were investigated numerically. As it has been shown in many studies, nanofluids provide better results for heat transfer applications compared to base fluids. In addition, nanofluids including especially metal or metal oxide nanoparticles are used in MHD flow applications because of their higher electrical conductivity. In this study, 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 0º-90º is used for application of external magnetic field. The problem geometry is a backward-facing step which is used in many engineering applications and flow separation and reattachment phenomenon occur in this geometry. Different convection effects of backward-facing step were examined with various values of Richardson number (Ri=0,01-0,1-1-10) which indicates the importance of natural or forced convection. Computations were made for pure water and four different nanoparticle volume fractions (ϕ=0,01-0,015-0,02-0,025) considering different electrical conductivity models. Finite element method via commercial code COMSOL was used for computation and results were shown with streamlines, isotherms and also Nusselt number variations for different values of pertinent parameters. 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.