Gradient microstructures for flow-boiling enhancement

Abstract

Herein, we apply grayscale lithography to produce novel gradient microstructures, demonstrating the enhancement of flow boiling through the manipulation of drag forces upon the forming bubbles. The use of engineered 3D anisotropy allowed directional control of boiling enhancement, with respective critical heat flux and peak heat transfer coefficient enhancements of up to 20% and 93% observed over the unstructured substrate. It is our suspicion that the sheltering of bubbles inside of cavity microstructures deteriorates their departure characteristics, and that the combination of induced turbulence and available surfaces to capture passing liquid is beneficial for protruding microstructures. We demonstrate the promising novel implementation of gradient microstructures in the boiling discipline, which may serve as a useful foundation for future work. The enclosed approach to boiling enhancement shows a potential future direction for engineered boiling microstructures, wherein bubble dynamics are directly manipulated on bespoke, 3-dimensional substrates, allowing the transfer of large heat fluxes at low wall temperatures.