Effect of Ball Milled and Sintered Graphene Nanoplatelets–Copper Composite Coatings on Bubble Dynamics and Pool Boiling Heat Transfer

Abstract

Herein, the efficacy of graphene nanoplatelets–copper (GNP–Cu) composite coatings formed by ball milling and sintering methods in enhancing the pool boiling, i.e., phase‐change heat transfer tested for distilled water, is presented. The pool boiling performance is quantified by an increase in critical heat flux (CHF) and heat transfer coefficient (HTC) at the lower wall superheat temperature. The ball milling facilitates the draping of highly thermally conductive GNP around individual copper particles and subsequent sintering results in morphological features that further promote high wicking rates of the coatings. A variety of coatings are formed with varying GNP concentrations and copper particle sizes. Highest pool boiling performance is achieved for the 2 wt% GNP and 20 μm diameter Cu coating, with a CHF of 239 W cm−2 and HTC of 285 kW m−2 °C−1, which indicate an increment of ≈91% and ≈438%, respectively, compared with a pristine copper surface. Stretched or elongated pores observed for certain compositions of the coatings, termed as “pore pockets” in this work, contribute in higher pool boiling heat transfer due to their ability to contain and supply liquid, while acting as nucleation sites for vapor generation and escape.