MHD effect on Nanofluid Flow and Heat transfer in Backward-Facing Step using two-phase Model

Document Type : Research Article

Authors

1 Department of Mechanical Engineering, Urmia University of Technology

2 Mechanical Engineering Department, Universite Laval, Quebec, Canada

Abstract

Magneto hydrodynamics (MHD) effects on nanofluid flow in backward-facing step is studied using two-fluid model of Buongiorno. The results of the current finite element simulations are compared with previous experimental and numerical analysis. Due to the utilization of two-phase model, variable nanoparticle concentration and nanofluid properties are considered. Thermophoresis and Brownian diffusivities are calculated in particle dispersion. Effects of Reynolds number, particle volume fraction, magnetic field and Hartmann numbers are studied on heat transfer and fluid flow characteristics. It is shown that introduction of nanoparticles as a second phase, pushes reattachment point further into the downstream, while magnetic field has opposite effect and pushes it backward into the upstream. Particles are shown to be migrating from hot to cold regions due to the dispersion mechanisms considered. In comparison to single phase models, there is 3.7% decrease in maximum Nusselt number and more than 40% difference in the reattachment point location. Accuracy of the reattachment point is shown through previous pure fluid studies, the comparison to which show less than 0.8% tolerance with most recent studies. Relative effect of diffusion mechanisms is compared in different flow conditions, which show up to 12.5% difference. Application of magnetic field results in average Nusselt number increase of more than 10% by Hartmann number of 12.

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