Abstract
Micro/nanostructure is a popular and effective structure for boiling heat transfer enhancement. In this study, ultrasonic cavitation modification is employed firstly to create microstructured aluminum surface for boiling heat transfer. With the impact of ultrasonic cavitation microjet, numerous micro pits and holes are formed on the surface in one step, constituting microstructures on aluminum plate. The saturated and subcooled pool boiling experiments are conducted at atmospheric pressure using ethanol as a working fluid. It is found that boiling hysteresis is apparent on the modified plate (MP) with the porous microstructure layer, which can be eliminated by periodically fluctuating heat flux. Under the stable saturated boiling condition, the maximum heat transfer coefficient is enhanced by 208% and wall superheat is decreased by 17.6 °C compared to the bare aluminum surface. Under subcooled boiling conditions, the boiling hysteresis on MP becomes weaker and the positive effect of microstructures on heat transfer performance is enhanced. The enhanced heat transfer coefficient of MP is mainly attributed to the increase of nucleation site density and further to the facilitation of bubble coalescence and departure, while the increased critical heat flux under subcooled boiling conditions is derived from the delaying occurrence of mushroom-like bubble.
Published Version
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