The effect of constant magnetic field on convective heat transfer of Fe3O4/water magnetic nanofluid in horizontal circular tubes

In this paper, the heat transfer and flow characteristics of Fe3O4/water magnetic nanofluids were experimentally studied under the effect of a magnetic field. The experimental results were combined with a magnetic flux density distribution. The effects of magnetic flux density, magnetic field gradient, and different magnetic field orientations on the local Nusselt number and flow pressure drop were analyzed. The results show that, increasing the magnetic flux density and magnetic field gradient can achieve a significant improvement in the convective heat transfer. At the Re of 1080 and the magnetic field of 415 gauss, the local Nusselt number for 0.5 vol% Fe3O4/water magnetic nanofluids increased by 4.36%, whereas the corresponding value for the magnetic field of 700 gauss increased by 7.19%. Additionally, the local Nusselt number increased by 32.0% under a magnetic field gradient of 28.6 gauss/mm. The occurrence of chain-like structure is the main reason for the increased convective heat transfer. In addition, the flow disturbance caused by the magnetic field increases the pressure drop. However, the effect is weaker than the enhancement of heat transfer.