Enhanced liquid replenishment for pool boiling heat transfer and its CHF mechanism on patterned freeze-casted surfaces

Abstract

In the current investigation, the pool boiling heat transfer process of patterned porous surfaces, as well as a smooth surface, in ethanol was examined from an academic perspective. The freeze casting (also known as ice-templating) processes was used to fabricate the structured surfaces. It was discovered that freeze-casted coatings significantly improved the performance of boiling heat transfer in comparison to the smooth surface (SMS). The most remarkable increase in Critical Heat Flux (CHF) was achieved by checkerboard porous surface(CHECKERBOARD), with an improvement of 81.6% relative to that of SMS. The maximum Heat Transfer Coefficient (HTC) enhancement was obtained by full porous surface (FULLY-COVERED), with an HTC value 215.8% higher than that of the SMS. For the semicircular porous surface (SEMICIRCULAR), striped porous surface (STRIPED), annular porous surface (ANNULAR) and checkerboard porous surface(CHECKERBOARD) with 50% coating coverage, CHECKERBOARD demonstrated the best heat transfer performance, with CHF and HTC increased by 32.3% and 48.9%, respectively, compared to the SEMICIRCULAR surface. The mechanism of liquid supply at the CHF of the patterned porous surfaces was investigated through phenomenological observations of the boiling phenomena. A modified model, accounting for the coalesced bubble departure frequency and capillary wicking effects, was proposed for CHF prediction. It is noteworthy that the fluid replenishment considers both vertical and lateral replenishment of porous coatings. The CHF data from this study, along with existing literature, were utilized to validate the model, and the predicted results exhibited good agreement with the experimental data, with errors within ±8%.