Investigation of heat transfer characteristics of magnetic nanofluids with forced convection in minichannels under magnetic field effect

In this thesis, the heat transfer characteristics of water-based magnetic nanofluids in minichannel under the effect of alternating and constant magnetic fields were investigated. The experiments were carried out at constant heat flux boundary conditions and laminar flow regime. Nanofluids were prepared by dispersing NiZnFe4O4 nanoparticles in pure water at 0.5% and 1% volumetric ratios. The experiments were carried out in the range of 300 – 1,300 Reynolds numbers. The effect of three different constant magnetic fields, with intensities of 22, 30 and 38 mT, on heat transfer was researched. In addition, the effect of alternating magnetic field with frequency 50 Hz and intensities of 3 and 5 mT on heat transfer was investigated. As a consequence of the experiments, a considerable increase was observed in the pressure drop and accordingly the friction factor as well as the heat transfer with the use of nanofluids. The heat transfer coefficient and Nusselt number exhibited remarkable increases with the nanoparticle volumetric ratio, Reynolds number and magnetic field intensity. While the magnetic field effect was more evident at low Reynolds numbers, this effect gradually decreased with increasing Reynolds number. In addition, the heat transfer performance of the nanofluid with a high volumetric ratio was affected by the magnetic field much more than the other.