Thermal Conductivity of $$\mathrm{Fe}_{2}\mathrm{O}_{3}$$ Fe 2 O 3 and $$\mathrm{Fe}_{3}\mathrm{O}_{4}$$ Fe 3 O 4 Magnetic Nanofluids Under the Influence of Magnetic Field

Abstract

In this paper, the thermal conductivity of water-based hematite $$(\mathrm{Fe}_{2}\mathrm{O}_{3})$$ and magnetite $$(\mathrm{Fe}_{3}\mathrm{O}_{4})$$ nanofluids have been investigated in the absence and presence of a uniform magnetic field. The experiments have been performed in the volume concentration range of 0 % to 4.8 % and the temperature range of $$20\,^{\circ }\mathrm{C}$$ to $$60\,^{\circ }\mathrm{C}$$ . The effects of the particle volume fraction, temperature, and magnetic field strength on the thermal conductivity have been analyzed. Results show that the thermal conductivity of iron oxide nanofluids has a direct relation with the particle volume fraction and temperature, without the presence of a magnetic field. But surprisingly, when the magnetic field is applied, it is observed that the thermal conductivity decreases with increasing temperature and it is also higher for a magnetite nanofluid than for a hematite nanofluid. Moreover, changes in the strength of the magnetic field cause the thermal-conductivity ratio of the ferrofluid with respect to pure water to increase from 15 % to 38.5 % and from 13 % to 175 % for magnetite and hematite nanofluids, respectively. Based on the obtained experimental results, a correlation has been developed for the thermal conductivity of iron oxide magnetic nanofluids as a function of the volume fraction, temperature, and magnetic field strength.