Vortex flow properties and enhanced heat transfer analysis of ferrofluid in a curved pipe under the coupling of magnetic field force and centrifugal force

In this study, the flow and heat transfer characteristics of ferrofluid in a 90 degrees curved tube with an applied external magnetic field are numerically investigated based on the finite element method. The flow field structure, generation mechanism of secondary flow, and heat transfer enhancement effect of the magnetic nanofluid under the coupling effect of magnetic field force (formed by the applied magnetic field) and centrifugal force (formed by the curvature of the curved pipe) are analyzed. Results show that a low-intensity magnetic field may slightly inhibit the heat transmission of ferrofluid in a curved pipe. As the strength of the external magnetic field increases, an evident secondary flow with three pairs of primary vortices is observed on the cross section. The secondary flow destroys the boundary layer, intensifies fluid mixing, and enhances heat delivery of the bent pipe. Within the studied range, the heat transfer coefficient with an external magnetic field increases by a maximum of 58.8 % compared with that without an external magnetic field. Moreover, the influence of magnetic field on heat exchange is more pronounced within smaller Reynolds numbers.