The flow and heat transfer performances of magnetic nanofluid in a duct in presence of magnetic fields with different direction

The flow and heat transfer characteristics of magnetic nanofluids in a circular channel under the action of magnetic fields were studied through numerical simulation based on the finite element method. The results show that there are obvious secondary vortices on the cross-section, and a swirling flow is formed in the duct under the coupling effects of the magnetic field, velocity distribution, and thermal variations which destroys the boundary layer, accelerates the mixing of fluids, and enhances heat transfer. In the studied range, the maximum heat transfer coefficient can be increased by 102.65 %, and the maximum comprehensive heat transfer factor J is 1.69 compared to the ferrofluid not affected by the external magnetic field. In addition, the effect of enhancing heat transfer gradually decreases with the increase of θ, until heat transfer is slightly inhibited when the magnetic field is parallel to the flow direction.