Effect of magnetic field and surfactant on the boiling heat transfer and CHF of magnetic nanofluids on a downward heating surface

In this study, boiling heat transfer experiments on downward heating surface with different concentrations of magnetic nanofluids (alpha-Fe2O3 and gamma-Fe2O3 nanofluids) was explored, through adding surfactants and applying external magnetic fields to enhance the critical heat flux (CHF). The CHF of each group of experiments was compared with that of the water condition. The results revealed that the surfactants cetyltrimethylammonium bromide (CTAB) and ethylene glycol (EG) as well as the magnetic field could improve the CHF of the magnetic nanofluid. And, surfactants improve the dispersion of the magnetic nanofluids. Specifically, under the magnetic field, 0.005 g/L of gamma-Fe2O3/EG-water nanofluid showed the largest CHF enhancement of 34.0 % compared to the aqueous condition. Furthermore, the mechanism behind enhancing CHF of magnetic nanofluids was discussed by analyzing the modification of nanofluids, the deposition on the heating surface, and the behavior of bubbles during the experimental process.