Scalable macroscale wettability patterns for pool boiling heat transfer enhancement

Abstract

Boiling utilizes latent heat of vaporization of the fluid to dissipate large amount of heat at small temperature budgets. Surfaces with micro−/nano-scale wettability patterns have been shown to improve the heat transfer coefficient during pool boiling. In this work, we propose a simple and cost-effective technique to fabricate heterogenous surfaces with macroscale wettability patterns comparable to the capillary length of the boiling fluid. We demonstrate that such surfaces can enhance boiling heat transfer coefficient significantly. Four configurations (two samples of hydrophobic dots and lines each) of heterogeneous surfaces are investigated to understand the influence of the diameter, pitch and arrangement of hydrophobic regions on the hydrophilic background surface on the heat transfer coefficient. Results indicate that up to ≈66% enhancement in the heat transfer coefficient can be achieved in comparison to the bare surface. If the hydrophobic dots are spaced out sufficiently, number of dots on the surface controls the heat transfer coefficient at low heat fluxes. However, nucleation is initiated even on the hydrophilic background surface at high heat fluxes and smaller diameter dots start performing better than the larger diameter dots. Smaller pitch (< bubble departure diameter) leads to lateral coalescence among the departing bubbles in case of lined pattern configuration, thereby lowering the heat transfer coefficient. The study demonstrates that simple and cost-effective macroscale wettability patterns can separate liquid supply and vapor removal pathways to enable comparable heat transfer coefficients enhancements otherwise achieved through sophisticated and costly surface patterning techniques discussed in literature.