Effect of nanoparticle polarization on relative permittivity of transformer oil-based nanofluids

Our experiments on a transformer oil-based nanofluid (NF) with ZnO nanoparticles reveal a higher relative permittivity than that of pure transformer oil. Meanwhile, the relative permittivity of ZnO NF presents a linear increase with nanoparticle volumetric concentration and a linear decrease with ambient temperature. A model based on nanoparticle polarization is proposed to investigate the mechanisms of NF relative permittivity. Analysis of the presented polarization model suggests that the value of the NF relative permittivity is dominantly determined by transformer oil, while the higher relative permittivity of NFs compared with that of pure oil is mainly caused by nanoparticle inner polarization.