Stability, thermo-physical and electrical properties of naphthenic/POME blended transformer oil nanofluids

Abstract

This study aims to investigate the stability, thermo-physical properties and electrical properties of pure transformer oil (naphthenic), palm oil methyl ester (POME) and blend oils suspended with SiO2-graphene nanoparticles. The hybrid SiO2-graphene was synthesized via sol–gel technique with pH varying from 10 to 12. Simultaneously, the transformer oil blend was prepared by homogenizing transformer oil and POME with various mass ratios ranging from 0 to 100%. Later, the nanofluids were synthesized by dispersing SiO2-graphene nanoparticles via high-speed homogenization (25000 RPM) followed by water bath sonication for 5 h. The stability of the nanofluids was measured by visual observation and UV–Vis spectrometer. Optimization of blend oils and hybrid nanofluids was performed using Minitab 18 for higher thermal conductivity and lower viscosity as the criteria for faster heat dissipation and fluid flow. Hybrid nanoparticles synthesized at pH 10 showed the lowest sedimentation rate than pH 11 and 12 and were therefore selected for further studies. Results show the thermal conductivity of nanofluids increased with hybrid nanoparticle concentration and temperature. The viscosity of nanofluid decreased with temperature with POME-based resulted in the lowest. Oxidation induction time (OIT) decreased with temperature but increased with the addition of hybrid nanoparticles. The optimized nanofluid blend was found to be 81.51 wt% mineral oil, 18.48 wt% POME and 0.10 wt% hybrid nanoparticle concentration. Further, the optimized sample resulted in lower dissipation dielectric factor than pure transformer oil. However, the breakdown voltage and resistivity of pure transformer oil is higher than optimized sample.