Properties of Mineral Oil based Silica Nanofluids

A nanofluid as intended for use in high voltage engineering is a heat transfer fluid, containing a small fraction of nano-sized filler materials. These nanoparticles exhibit unique properties, compared to those of the same material at the bulk scale. The term "nanofluid" was coined by Choi et al. at Argonne National Laboratory and refers to a colloid fluid, composed of a liquid phase and dispersed nanoparticles in suspension. Nowadays, nanofluids are considered the next generation of heat transfer fluids due to their improved heat transfer properties, compared to conventional fluids. In HV applications nanofluids based on mineral oil are being studied, to determine if they are a suitable replacement for conventional transformer oil or vegetable oil. In this study, mineral oil based silica nanofluids with different concentrations were prepared. The AC breakdown voltage of the nanofluids was tested at different moisture content levels. Silica nanofluids exhibit improved breakdown strength, especially at high moisture content level. The thermal conductivity was measured in the temperature range 10°C to 80°C, with up to 0.1% silica nanoparticles. Despite the reputation of nanofluids of being superior heat transfer fluids, only a negligible effect on the thermal conductivity of mineral oil could be found.