Transformer oils-based graphene quantum dots nanofluid as a new generation of highly conductive and stable coolant

Transformer oil-based graphene quantum dots (GQD) nanofluid with superior colloidal stability has great potentials as a new generation of high performance transformer oil. To this end, graphene quantum dots were initially synthesized with a novel and cost-effective exfoliation approach. To eliminate the acidity, a covalently-functionalization process was employed to change GQD to amine-treated graphene quantum dots (AGQD). The morphological analysis confirmed that the diameter and average height of the mono-layered AGQD were mostly in the range of 5-17 nm and <1 nm, respectively. Transformer oil-based AGQD nanofluid at very low weight fraction has been shown experimentally to have substantially higher positive voltage breakdown, thermal conductivity, natural and forced heat transfer rate, and flash point levels compared to that of pure transformer oil. A comprehensive rheological and electrical analysis of the transformer oil-based AGQD nanofluid showed no significant enhancement in its viscosity compared to pure transformer oil, which is a great advantage of this new generation of transformer oil. Case studies showed that the transformer oil-based AGQD nanofluid has a superior colloidal stability, offering improved high voltage equipment performance and reliability. (C) 2017 Elsevier Ltd. All rights reserved.