Ferrofluid Flow and Heat Transfer From a Sphere in the Presence of Nonuniform Magnetic Fields

In this article, the effects of nonuniform magnetic fields on the hydrodynamics and heat transfer from a heated sphere to its surrounding ferrofluid flow have been investigated. Kelvin body forces originate from the nonuniformity of the applied magnetic field and can generate the vortices behind the sphere leading to a considerable change in the velocity and temperature fields. The applied magnetic field disturbs the thermal boundary layer and decreases heat-transfer resistance, leading to a significant enhancement in the heat-transfer coefficient. Variations of the local and average Nusselt number value (Nu), separation angle, recirculation length, and drag coefficient were considered to investigate the effects of magnetic field intensity, Reynolds number, and the relative magnetic permeability of the sphere. In addition, the arrangement of the coils was optimized to provide the highest heat-transfer rate. Moreover, the obtained results indicate that enhancement in Nuavg is much larger than the drag resistance penalty.