Microlayer evaporation governs heat transfer enhancement during pool boiling from microstructured surfaces

Enhancement of the rate of boiling heat transfer, a critically significant need across a range of industrial transport processes, can be achieved by the introduction of surface microstructures. However, the precise mechanism of such enhancement is not definitively understood. We establish microlayer evaporation from the imbibed liquid layer underneath the growing vapor bubbles as the key mechanism of enhancement in boiling heat transfer coefficient for microstructured surfaces. We experimentally characterize nucleate boiling heat transfer performance on silicon surfaces custom-fabricated with controlled microstructures using HFE-7100 as the working fluid. We then undertake an analytical prediction of the microlayer evaporation from the microstructured surface. A clear dependence of the measured boiling heat transfer coefficients from microstructures of different dimensions on the predicted evaporation heat transfer coefficients allows us to conclude that microlayer evaporation governs the boiling enhancement from microstructured surfaces.