Numerical investigation of effects of uniform magnetic field on heat transfer around a sphere

In this article, ferrohydrodynamic forced-convection heat transfer from a heated sphere embedded in a ferrofluid in the presence of the uniform external magnetic field has been studied numerically for the first time over a wide range of Reynolds number value, nanoparticle diameter, particle volume fraction, and magnetic field intensity. Despite the uniform external magnetic field applied, the internal magnetic field near the sphere could be nonuniform due to the considerable difference between the relative magnetic permeability of the sphere and the surrounding medium. Kelvin body force arises from this nonuniformity and induces vortexes near the sphere. These vortexes disturb the boundary layer, decrease the heat-transfer resistance, and enhance the heat-transfer rate. Variations of the local Nusselt number value were investigated to examine the effects of aforementioned parameters. The obtained simulation results indicate that the average Nu value strongly depends on the magnetic field intensity. Furthermore, the simulation results obtained for drag coefficient and Nu values were validated against those reported in the literature in the absence of magnetic field. The obtained simulation results were successfully correlated with Reynolds and Prandtl numbers.