Enhancement of thermal conductivity of kerosene-based Fe3O4 nanofluids prepared via phase-transfer method

Phase-transfer method has been applied for preparing stable kerosene based Fe3O4 nanofluids. Oleic acid was successfully grafted onto the surface of Fe3O4 nanoparticles by chemisorbed mode, which let Fe3O4 nanoparticles have good compatibility with kerosene. Pure cubic-phase Fe3O4 nanoparticles with an average diameter of 15 nm were obtained. The nanoparticles in nanofluids had the tendency to form larger clusters with the diameter of about 155 nm, and ultrasonication could not decrease the size of the clusters. The Fe3O4 nanofluids prepared by phase-transfer method do not show the previously reported “time-dependence of the thermal conductivity characteristic”, which indicates the stability of the nanofluids. In the temperature range from 10 to 60 °C, the thermal conductivities of the nanofluids track the thermal conductivities of the base liquid and the enhanced ratios are almost constant for the same loading. There is no clear behavior of the previously reported “the temperature dependence of the thermal conductivity”. The enhancement of the thermal conductivity increases linearly with the volume fraction of Fe3O4 nanoparticles and the value is up to 34.0% for 1.0 vol.% nanofluid. It is proposed that the soft cluster structure may be the reasonable explanation of the anomalously enhanced thermal conductivity.