Enhanced boiling heat transfer by nucleation patterning with self-assembly of reduced graphene oxide coating

Boiling heat transfer is a favorable method for cooling high heat flux devices, and its performance is evaluated using critical heat flux (CHF), which indicates the maximum heat dissipation capacity. CHF occurs when a surface is covered with a vapor film due to bubble coalescence. Here, we propose a new nucleation patterning surface using rGO-coated micropillar-free cavities in order to enhance boiling heat transfer by suppressing bubble coalescence. Nucleation patterned surface is achieved by a sectored self-assembly on surfaces with artificial cavities embedded in micropillar array. The nucleation pattern is designed with spacings of 1.0 and 1.5 mm, with reference to the bubble departure diameter on the rGO-coated micropillar surface. The rGO particles deposited on the bottom of the micropillar-free cavity cause bubble formation in the cavities, and the micropillars around the cavities supply liquid to bubbles through wicking. Moreover, rGO deposition with varying heat flux schemes suggests the capability of constructing toned rGO layers on patterned micropillar surfaces. The results confirmed that high heat transfer performance can be obtained by applying denser bubble nucleation with a bubble generation spacing to bubble departure diameter ratio of 1, under the condition of preventing bubble coalescence. The heat transfer coefficient and critical heat flux were augmented by 340% and 203%, respectively, by preserving flow paths for water imbibition under the floating rGO layer and delaying bubble coalescence.