Superior boiling performance of multiscale microporous surfaces and the underlying mechanisms

초록

Boiling heat transfer has emerged as a promising technology for high-density electronic chip cooling owing to its superior heat-removal capability. In this study, we investigate the pool boiling performance and underlying physical mechanisms of multiscale microporous surfaces fabricated via commercial-grade copper (Cu) particle sintering using high-speed visualization and infrared (IR) thermometry techniques. Seven substrates were examined, including three smooth surfaces (SiO2, aged SiO2, and smooth Au) and four sintered microporous surfaces, fabricated with or without millimeter-scale pillars and with or without thermal oxidation. The microporous sintered surfaces showed superior boiling performance in terms of the critical heat flux (CHF) and boiling heat transfer coefficient (BHTC). The microporous surface with a pure Cu porous layer achieved a maximum BHTC of 202.5 kW/m2K (approximate to 414% of that of bare SiO2), while pillar-structured microporous surfaces achieved CHFs of similar to 4 MW/m2 (approximate to 400% of that of bare SiO2) by promoting spatial separation of vapor-liquid flow pathways and enhanced capillary-driven liquid supply. IR thermometry revealed that local hot spots in the pre-CHF condition could be rewetted by a capillary-driven liquid supply on the microporous surfaces. In contrast, the CHF is triggered when local dry spots (hot spots) expand irreversibly, leading to rapid temperature excursion and burnout within 10-100 ms. The study highlights that nanostructured microporous surfaces exhibit faster rewetting dynamics than those of porous surfaces without nanostructures, which are attributed to the enhanced capillary wickability of CuO nanorods. These results demonstrate that multiscale (nanometer, micrometer, and millimeter scales) sintered microporous structures offer a practical and scalable solution for ultra-high heat flux boiling applications with improved thermal stability and temperature uniformity.

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