Prediction of Heat Transport and Drag Force of Ferrofluids around a Sphere in the Presence of Oscillating Magnetic Field

Abstract

In this article, the heat transfer of magnetic nanofluids over a sphere has been considered in the presence of an external oscillating uniform magnetic field for various range of Reynolds number (Re). The significant difference between the magnetic property of the nanofluid and the heated sphere makes a non-uniform magnetic field around the sphere resulting a significant alteration in the distribution of velocity and temperature around sphere. The variations of average Nusselt number (Nuavg) and drag coefficient (Cd) have been studied to demonstrate the influence of magnetic field frequency and intensity, Re and the relative magnetic permeability of the sphere. It has been found that the magnetic field causes the vortices to appear or grow behind the sphere. These vortices lead to boundary layer distortion and thereby increasing heat-transfer rate and drag force. In addition, the obtained results clearly indicate that there is an optimal frequency at which Nuavg and Cd can be maximized. Moreover, the influence of the applied magnetic field is more noticeable for low Re values and/or frequencies near the optimum value. Furthermore, the obtained results clearly demonstrate that the heat-transfer increase is much higher than the penalty due to the drag force increase for frequencies close to the optimal value.