Carbon nanostructures-based transformer oil nanofluids as coolants with enhanced performance

Transformer oil (TO) is a highly pure oil that has high durability at high temperatures and is a superior electrical insulator. TO is utilized as insulation and coolant. One of the common problems of TO is overheating, especially in warm seasons, which reduces the efficiency of the transformer, power outages, etc. In this research, heat transfer coefficient, dimensionless numbers, dielectric breakdown voltage, and physical properties of nanofluids were investigated to improve the efficiency of the transformer by adding nanofluids, including graphene nanoplatelets (GNP) and multi-walled carbon nanotubes (MWCNT) to TO. The results showed that the natural convective heat transfer coefficient (NHTC) of 0.005%wt GNP/TO increased 8.6% and 12.8% compared to pure TO and 0.005%wt MWCNT/TO, respectively. Besides, the forced convective heat transfer coefficient (FHTC) of 0.005%wt GNP/TO enhanced by 8.3% and 9.0% compared to pure TO and 0.005%wt MWCNT/TO, respectively. Dielectric breakdown voltage in GNP/TO and MWCNT/TO nanofluids decreased compared to pure TO due to free electrons. The density of TO also increased by adding GNP and MWCNT. The thermal conductivity of GNP/TO nanofluid was also higher than pure oil and MWCNT/TO and increased by rising temperature, while the thermal conductivity of natural transformer oil was reduced by raising the temperature.