Anomalously enhanced thermal performance of micro heat pipes coated with heterogeneous superwettable graphene nanostructures

Abstract

The thermal performance enhancement of micro heat pipe (MHP) array attributed to the incorporation of graphene nanoplatelets (GNPs) coatings with different wettability is investigated. The wettability of GNPs can be tuned to superhydrophilic and superhydrophobic via functionalization under thermal treatment. The micro/nano porous structures and ultrafast water transport property of the functionalized GNPs coatings are favourable to the three primary operational processes of an MHP, i.e., evaporation, condensation and circulation of working fluid. By coating superhydrophilic GNPs to the evaporator and superhydrophobic GNPs to the condenser, the evaporation and condensation strength can be simultaneously enhanced. The ultrafast water transport property of GNPs also provides nanocapillary effect which significantly enhances the circulation rate of working fluid. The combined enhancement of evaporation, condensation, and fluid circulation synergistically leads to anomalous thermal performance enhancement of MHP. By benchmarking with the uncoated MHP, the overall performance of a heterogeneous-wettability-coated MHP, as quantified by its effective thermal conductivity, manifests a maximum enhancement of 307%. An enhancement of 206% in the heat transfer coefficient and a dramatic temperature drop of 45 °C of the heated surface are achieved. To elucidate the underlying mechanism leading to the anomalous performance enhancement, molecular dynamics simulations are performed to investigate the ultrafast water transport through the superwettable GNPs nanostructures. This study paves the way for promising applications of heterogeneous superwettable GNPs nanostructures in micro-scale capillary-driven devices for electronics cooling.