Boiling offers an effective means of high heat flux dissipation for thermal management of electronics, power plants, and nuclear reactors. Critical heat flux (CHF) is a catastrophic failure mechanism in boiling and imposes an operating limit for these applications. Past studies have extensively explored the use of microstructured surfaces to increase the CHF limit by promoting capillary wicking of the working fluid to the surface. Existing models for predicting this CHF enhancement are developed by assuming a monotonic scaling between boiling CHF and the wicking ability of the microstructures. Our recent analytical model introduced the competing mechanism of evaporation from the microstructures, which revealed that the coupled evaporation and wicking characteristics of a structured surface together play an important role in governing the CHF enhancement. In the present work, we validate the CHF model developed earlier by performing pool boiling experiments with HFE-7100 on square silicon micropillar arrays having controlled geometries that allow exploration of both evaporation-limited and wicking-limited regimes. The experimental results confirm the existence of an evaporation-limited CHF regime in which increases in the wicking ability of the structures do not lead to higher CHF. In contrast to predictions of prior wicking-based models, we observe a non-monotonic trend in CHF with variation in the size of the microstructures due to the coupling between wicking and evaporation. The model is further used to produce optimal design guidelines for maximixing the CHF enhancement through micro-structuring of boiling surfaces.


Experimental Demonstration of the Coupling Between Wicking and Evaporation During Critical Heat Flux on Structured Surfaces

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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