Experimental investigation on laminar convective heat transfer of nano ferrofluids under constant and alternating magnetic field

Due to unique characteristic behavior of ferrofluids, their rheological and thermophysical properties will be able to change in the external magnetic field. In this paper, the effects of constant and alternating magnetic field on the convective heat transfer coefficient of ferrofluids in a heated circular tube under laminar flow regimes (200≤Re≤1600) are investigated experimentally. The fluids considered in the experiment are distilled water and a Fe3O4/water nanofluid with 1% and 3% concentrations by weight (wt%). The obtained results are validated and a good agreement between the experimental data and predicted results is observed. In the absence of a magnetic field, the results illustrate the significant improvement of convective heat transfer for 3 wt% ferrofluid, compared to that of the distilled water as a working fluid. The heat transfer enhancement varies by changing the Reynolds number as well as ferrofluid concentration and the type of applied magnetic field. The results also show that with application of alternating magnetic field with frequency of 50 Hz, the maximum of 5% enhancement in the convective heat transfer coefficient is obtained compared to the case with no magnetic field.