FHD and MHD effects of Fe ₃ O ₄ -water magnetic nanofluid on the enhancement of overall heat transfer coefficient of a heat exchanger

Abstract

Abstract The electrically conducting magnetic nanofluid of Fe 3 O 4 -water was made to flow in a heat exchanger. Afterwards, the ferrohydrodynamics (FHD) and magnetohydrodynamics (MHD) effects of the nanofluid on the enhancement of the overall heat transfer coefficient of the heat exchanger were studies at different nanofluid concentrations, inlet temperatures, and different constant magnetic field intensities. The study dealt with both laminar and turbulent nanofluid flows. The electrical conductivity of the magnetic nanofluid was determined by a Jenway 4510 conductivity meter. By using the experimental data, a Sprint CFD code identified the hydrodynamic and thermal behavior of the nanofluid flow in the presence of constant magnetic fields of intensities of 0, 0.05, 0.1 and 1 Tesla. The results showed that an increase in the concentration of Fe 3 O 4 -water nanofluid enhanced its electrical conductivity so considerably that the nanofluid, at the volume fraction of 1%, was observed to be 12.5 times more electrically conductive than distilled water. Also, it was shown that increase in magnetic field intensity had an enhancing effect on the overall heat transfer coefficient, and the effect was stronger at higher magnetic nanofluid concentrations. Furthermore, due to generation of chainlike structures by the FHD effect of the Fe 3 O 4 magnetic nanoparticles, the nanoparticles increased the effective thermal conductivity of the nanofluid and, consequently, the overall heat transfer coefficient in both the laminar and turbulent regimes. Finally, unlike the turbulent flow, the laminar regime allowed for the MHD effect having only a negligible effect on the enhancement of the overall heat transfer coefficient. This was due to velocities in the laminar regime being small.