Critical heat flux (CHF) is a catastrophic failure mechanism in boiling and imposes an operating limit for thermal management in electronics, power plants, and nuclear reactors.  Recently, microstructured surfaces have shown great promise in increasing the CHF limit by promoting capillary wicking of the working fluid to the surface. Existing models for predicting 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. Therefore, understanding the evaporative heat transfer performance of a structured surface is a critical step toward predicting CHF. In the present work, we develop a figure of merit (FOM) that characterizes the evaporative heat transfer performance of microstructured surfaces. The developed FOM is using effective properties, such as contact line length per unit area and porosity, that can be simply calculated for any general surface morphology. The FOM is calibrated against an effective evaporative heat transfer model and later compared with evaporative heat transfer data in the literature. The FOM successfully captures the variation in performance across different structures, as well as successfully identifies the optimum parameters for a given structure type. Therefore, this figure of merit can serve as an initial design tool to survey different structures and optimize their morphologies for evaporative performance, an integral component of predicting CHF performance. This work will help produce optimal design guidelines for maximizing 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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