Effect of alternating magnetic field on unsteady MHD mixed convection and entropy generation of ferrofluid in a linearly heated two-sided cavity

This work considers the numerical study of unsteady MHD convection of cobalt-kerosene ferrofluid in a linearly heated two-sided cavity and in the presence of constant and alternating magnetic fields. An accurate finite volume method is adapted to solve the governing equations for this problem. The fluid flow and heat transfer characteristics are studied for a wide range of Richardson numbers (0.01 <= Ri <= 10) and Hartmann numbers (0 <= Ha <= 100). The volumetric fraction of nanoscale ferromagnetic particles in ferrofluid also varies between 0.0 <= phi <= 0.2, while the size of those nanoparticles is fixed at 45 nm. In addition, different alternating magnetic fields with various periods and phase deviations are utilized to study the effect of time-periodic magnetic field on the flow characteristics and heat transfer. The entropy generation and Bejan number are also evaluated to study the effect of key parameters and temporal variation of magnetic field on various fluid irreversibilities. The results show that applying time-periodic magnetic field has remarkably influenced the fluid characteristics, the fluid irreversibilities, and heat transfer within the cavity. Meanwhile, the influence of phase deviation on heat transfer seems to be insignificant. (C) 2017 Sharif University of Technology. All rights reserved.