Simulation of Variable Magnetic Field Effect on Natural Convection Heat Transfer of Fe3O4/Graphite Slurry based on Experimental Properties of Slurries

Abstract

Natural convective heat transfer of Fe3O4/graphite slurry in a square cavity is numerically examined. The slurry is assumed to be a non-Newtonian ferrofluid under a variable external magnetic field. The left and right walls of the cavity are assumed to be at a relatively low temperature (Tc), while the horizontal walls are thermally insulated. A heat source with a variable temperature distribution is located at the bottom of the enclosure. The non-Newtonian behavior of the graphite slurry (a mixture of ethylene glycol and graphite powder) has been modelled using experimental results. The control volume method and the SIMPLE algorithm were used to discretize and solve the governing equations considering the Ferro-hydrodynamics (FHD), the Magnetohydrodynamics (MHD) and the non-Newtonian fluid behavior. The heat transfer and fluid flow properties are determined for different locations of the magnetic field source, and different values of the magnetic number (Kelvin force), and the Hartmann number (Lorentz force). The results show that when the magnetic field source is located below the enclosure and near the heat source, the vortices are strengthened resulting in an increased heat transfer. The heat transfer rate is affected by FHD and MHD. When the magnetic field source is located at the corner points, the heat transfer rate is not significantly affected by the magnetic and Hartmann numbers. However, once the magnetic field source is located near the central point of the lower wall of the enclosure, the heat transfer rate is influenced by the increase of the magnetic number.