Abstract: The effect of magnetic field on the convective heat transfer of Fe3O4/Water nanofluids was experimentally studied. The Fe3O4/Water nanofluids flowed through a horizontal circular tube under the turbulent flow regime conditions. The pressure drop of Fe3O4/Water nanofluids was measured at volume fraction of 3%. The mechanism of the heat transfer of magnetic nanofluids under the magnetic field was discussed. The experimental results showed that the heat transfer coefficient increased with the increase of the Fe3O4/Water nanofluids concentration, and the maximum averaged enhancement was 4.3%. In the presence of the perpendicular uniform magnetic field, almost no obvious enhancement of the convective heat transfer coefficient of Fe3O4/Water nanofluids was observed in fields up to 23.809 and 39.682kA/m but it was observed in fields of intensity up to 63.492kA/m. The maximum averaged enhancement was 3%. Compared with the pressure drop of the distilled water, 50% enhancement was observed using Fe3O4/Water nanofluids at the volume fraction of 3%. Enhancement was also obtained under the applied magnetic field and the maximum averaged enhancement was 11.3%. The power ratio was less than 1, and thus the utilization of Fe3O4/Water nanofluids in heat transfer could not save energy.

Key words: nanofluids, heat transfer enhancement, magnetic field, pressure drop, energy ratio