Enhanced nucleate boiling using a reduced graphene oxide-coated micropillar

Abstract

Critical heat flux (CHF) enhancement is necessary in order to ensure a high operating limit for two-phase cooling applications. As the boiling is developed, formation of vapor film layer becomes vigorous, which causes CHF. Here, a graphene-coated micropillar structure (GMS) is proposed in order to enhance boiling heat transfer by suppressing vapor film formation on the surface. The GMS is designed to separate the bubble nucleation region from the liquid supply region in order to enhance CHF. By controlling the height of the micropillar, we obtained a structure in which the rGO layer is coated at the top of the micropillar array with high aspect ratio of the micropillar. In particular, the GMS consists of a reduced graphene oxide (rGO) porous mesh layer and a micropillar array layer. The rGO porous structure facilitated bubble nucleation by providing a suitably sized cavity. The micropillar array, which has excellent wicking performance, is located below the rGO porous layer in order to provide a capillary pumping to the vapor bubbles. Consequently, the GMS provides a significantly improved heat transfer coefficient and CHF of 288% and 152%, respectively, compared to the plain surface.