Influence of a nonuniform magnetic field on the flow and heat transfer of a thermosensitive ferrofluid

In this work, we numerically investigate how a nonuniform magnetic field affects the flow and heat transfer in a bottom-heated closed enclosure filled with a thermosensitive ferrofluid. Under the simultaneous action of the gravitational and external magnetic field, a complex flow develops inside the cavity. We change the intensity of the external magnetic field aiming to understand how the flow field, temperature distribution, and net heat transfer are affected. Our findings reveal that the magnetic field has a significant influence on the topology of the flow and temperature fields, consequently impacting the overall heat transfer. It is possible to use the magnetic field generated by a conducting wire to change the net heat transfer through the cavity. We found that the average Nusselt number is a growing function of the magnetic field intensity, except for a specific Rayleigh number. Furthermore, we recognize non-stationary regimes at intermediate magnetic Rayleigh numbers, associated with unstable topological transitions in the flow pattern induced by the magnetic field. Consequently, we uncover flow regimes characterized by steady boundary conditions but exhibiting periodic flow and heat transfer patterns. Additionally, we observe that the unsteady topological transitions are suppressed by high magnetic Rayleigh numbers, resulting in steady flow.