Heat transfer enhancement of ferrofluid flow within a wavy channel by applying a non-uniform magnetic field

This paper presents the effects of a non-uniform magnetic field on the hydrodynamic and thermal behavior of ferrofluid flow in a wavy channel by 3D numerical simulation. The wavy surfaces at the top and bottom of the channel are heated by constant heat fluxes. Moreover, the sidewalls are adiabatic. In the wavy section, in the perpendicular direction of the main flow, the magnetic field that linearly varies along the direction of the main flow is applied. The mathematical model that is consistent with the principles of ferrohydrodynamics and magnetohydrodynamics is used for the problem formulation. The results indicate that the wavy wall enhances the heat transfer rate on the bottom of the channel in comparison with the plain wall, while it does not have any significant effect on the top wall where the natural convection is weak. Furthermore, it can be found that the influence of the magnetic field on the flow field and heat transfer in the channel with the wavy walls is greater than one for the channel with the plain walls. This is due to the elimination of the recirculation zones in the sinusoidal cavities of the wavy walls by applying the magnetic field. The rise of the magnetic gradient value from 0 to 1.5 x 10(5) increases the skin-friction factors on the top and bottom wavy walls by factors of 11 and 1.6, respectively. In addition, it changes the Nusselt number 40% and 300% for the bottom and top walls, respectively.