Experimental investigation on thermal performance of covalently functionalized hydroxylated and non-covalently functionalized multi-walled carbon nanotubes/transformer oil nanofluid

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The study investigated the effect of adding covalently functionalized-hydroxylated multi-walled carbon nanotubes (MWCNTs-OH) and non-covalently-functionalized MWCNTs on the breakdown voltage and thermal properties of transformer oil in a rectangular chamber. The novelty of the present study is the use of covalently functionalized hydroxylated and non-covalently functionalized multi-walled carbon nanotubes in transformer oil, and the reason for the selection of these nanoparticles is the high intrinsic thermal conductivity compared to other nanoparticles. Between both studied nanofluids, the thermal and electrical performance of covalently functionalized MWCNTs-OH was better due to the highest increase in heat transfer coefficient of free transfer and using fan was related to covalently functionalized MWCNTs-OH, which increased by 26.23% and 30.08%, respectively. Also, by measuring the breakdown voltage, it was found that the MWCNTs-OH of 0.001 wt% had the lowest reduction compared to the base fluid and was equal to 55.6 kV, which showed good performance because the specified standard for transformer oil breakdown voltage property is between 30 kV and 70 kV. According to the results, covalently functionalized hydroxylated MWCNTs-OH/transformer oil nanofluid has better thermal performance than pure oil, which prevents the transformer from rising in temperature and can also be used as electrical insulation in transformers.