High-heat-flux dissipation technologies, such as two-phase heat sinks, are critical for thermal management of next-generation wide bandgap power electronics. Flow boiling instabilities are known to generally reduce the heat transfer and pressure drop performance of microchannel heat sinks. However, the effect of instabilities on the overall heat transfer coefficient and critical heat flux has not been fully quantified. One of the primary causes of flow boiling instabilities is the presence of system compressibility located upstream of the heat sink inlet. This compressibility can be in the form of air trapped within flow components, flexible tubing, or a large volume of subcooled fluid. In this study, flow boiling experiments are performed in a square cross-section microchannel under controlled levels of upstream compressibility. The impact of flow boiling instabilities on heat transfer coefficient and critical heat flux is characterized through analysis of both time-averaged steady state data as well as high-frequency pressure signals synchronized with high-speed visualization. The dielectric working fluid HFE 7100, with a saturation temperature of 60°C, is used in all experiments. The occurrence and effect of flow instabilities in three different channel sizes (widths of 1, 0.75, and 0.5 mm) is related to the degree of two-phase flow confinement.


Impact of Flow Boiling Instabilities on Heat Transfer Coefficient and Critical Heat Flux in a Microchannel

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

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

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