Abstract
Nanoparticles enhance the electrical insulation and thermal properties of vegetable oil, and such improvements are desirable for its application as an alternative to traditional insulating oil for power transformers. However, the traditional method of insulating nanofluids typically achieves high electrical insulation but low thermal conductivity. This work reports an environmentally friendly vegetable oil using exfoliated hexagonal boron nitride (h-BN) showing high thermal conductivity and high electrical insulation. Stable nanofluids were prepared by liquid exfoliation of h-BN in isopropyl alcohol. With 0.1 vol.% of the nano-oil, the AC breakdown voltage increased by 18% at 25°C and 15% at 90°C. Both the positive and negative lightning impulse breakdown voltages of the nano-oil were also enhanced compared with those of the pure oil. Moreover, the thermal conductivity of the nano-oil increased by 11.9% at 25°C and 14% at 90°C. Given its high thermal conductivity, the nano-oil exhibited faster heating and cooling effects than the pure oil. Nano-oils with an electric field (either DC or AC) displayed a faster thermal response than that without an electric field. The reason is that h-BN is oriented under the electric field and formed a thermal network to increase the heat transfer.
Highlights
Nanofluids, formed by adding nanoscale particles to the base fluid, are stable and homogenous suspensions that present advanced performance of electrical insulation and thermal conductivity [1,2,3,4,5,6]
The size of the exfoliated hexagonal boron nitride (h-BN) nanoparticles was mostly irregular, and the length ranged from few hundreds of nanometers to one micrometer
The thermal conductivity of the h-BN nanosheets is closely related to the number of layers [27]
Summary
Nanofluids, formed by adding nanoscale particles to the base fluid, are stable and homogenous suspensions that present advanced performance of electrical insulation and thermal conductivity [1,2,3,4,5,6]. Vegetable oil, which is a new kind of environmentally liquid dielectric, has drawn attention as a potential alternative to traditional mineral oil for power transformers in electric engineering [11]. Improving insulation and thermal conductivity of vegetable oil is a benefit to reduce the size of power transformer and improve long-term stable operation. Nanofluids with long-term stability are the basis for ensuring improved physical and electrical properties as well as heat transfer performance. Most literature reported that the nanofluids prepared by two-step method have a good stability [12, 13]
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