INVESTIGATING THE EFFECTS OF Fe3O4 NANOPARTICLES CONCENTRATION AND THE INTENSITY OF HOMOGENEOUS ALTERNATING MAGNETIC FIELD ON POOL BOILING

Abstract

Ferrofluids strongly enhance heat transfer in boiling phenomenon by changing the physical properties of the base fluid. The results will be impressive when the alternating magnetic field with regular frequency is applied to the ferrofluid boiling process. In the present research, pool boiling experiments were conducted using Fe₃O₄/water ferrofluid at three volume concentrations of 0.01%, 0.05%, and 0.1% in two cases. The heater was a nickel-chromium wire with a diameter of 0.1 mm. The alternating magnetic field was generated by a pair of Helmholk coils. The results indicated that the onset of nucleate boiling (ONB) was delayed by increasing the concentration of nanoparticles in the base fluid due to the deposition of nanoparticles and reducing the bubble formation process. Moreover, an increase in CHF (critical heat flux) was observed with an increase in the concentration of nanoparticles from 7% to 46% due to the increase in the deposition on the heater surface. The heat transfer coefficient increased at low concentrations and decreased with increasing concentration. Hence, applying the magnetic field showed that the ONB is accelerated due to more fluid mixing, more homogeneous temperature distribution and, as a result, more heat transfer. Applying Lorenk force by an alternating magnetic field on ferrofluid particles and alternatingly changing its direction resulted in greater fluid circulation and the reduction of bubble retention time around the heater. As a result of more heat transfer and a decrease in the temperature of the wire heater, the heat transfer coefficient showed a significant increase.