The influence of the magnetic field on the convective heat transfer characteristics of Fe3O4/water nanofluids

The effect of perpendicular, uniform and gradient magnetic field on the convective heat transfer of Fe3O4/water nanofluids in a turbulent flow regime were experimentally studied. The local convective heat transfer coefficients were measured at volume concentrations of 0.5, 1, 2 and 3% and temperatures of 20, 30 and 40 degrees C. It showed that the heat transfer coefficient increased with the increase of the Fe3O4/water nanofluids concentration, temperature and magnetic field intensity. In addition, the enhancement increased under the gradient magnetic field than that under the uniform magnetic field. Without the effect of the magnetic field, the maximum averaged convective heat transfer coefficient of Fe3O4/water nanofluids over that of Distilled Water was improved by 5.2% at the volume concentration of 3% and the temperature of 40 degrees C. When the uniform magnetic field (H = 800G) and gradient magnetic field (H-max = 800G, dH/dx = 0.1 T/m) were applied to the Fe3O4/water nanofluids, the maximum averaged enhancements of the convective heat transfer coefficient over that of in the absence of the magnetic field were 4.2% and 8.1%, respectively, at the volume fraction of 3% and temperature of 40 degrees C. Based on the non-dimensional analysis of the energy equation for ferrofluids, the effect of the magnetic field rather than that of the thermal motion of magnetic nanoparticles was dominant on the thermal transfer performance of Fe3O4/water nanofluids. The experimental results agreed well with the non-dimensional analysis. (C) 2017 Elsevier Ltd. All rights reserved.