A critical review on thermal conductivity enhancement of graphene-based nanofluids

Nanofluids which consist of nanoparticles added to conventional fluids (or base fluids) are considered as promising heat transfer fluids. Compared to metal, metal oxide nanoparticles and carbon nanotubes, graphene with its extremely high intrinsic thermal conductivity became the best candidate to design nanofluids. Such nanofluids have the potential to be highly-efficient heat transfer fluid by reducing loss of heat and increasing cooling rates. Over the last ten years, graphene-based nanofluids have shown significant thermal conductivity enhancements, however due to the numerous and interlinked parameters to consider, optimisation of their efficiency is still challenging. The present review article analyses and discusses the reported thermal conductivity in term of performance with respect to the amount of the used graphene to develop the prepared nanofluids. The enhancement of thermal conductivity must meet the minimal graphene amount due to its production cost and because graphene nanoparticles induces high viscosity in the nanofluid leading to higher energy consumption for the heat transfer systems. Unprecedented in the literature, this work proposes a simple approach to quantitatively compare the enhancement of the thermal conductivity of the nanofluids. The thermal conductivity performance parameter introduced could be applied to all nanofluid families and may become a reference tool in the nanofluid community. Such tool will help to determine the optimal preparation conditions without compromising the superior thermal performances.