Characterization of thin film evaporation in micropillar wicks using micro-Raman spectroscopy

Abstract

Thin film evaporation on microstructured surfaces is a promising strategy for high heat flux thermal management. To enhance fundamental understanding and optimize the overall heat transfer performance across a few microns thick liquid film, however, requires detailed thermal characterizations. Existing characterization techniques using infrared thermometry or contact-mode temperature sensors such as thermocouples and resistance temperature detectors cannot accurately measure the temperature of the thin liquid film near the three-phase contact line due to the restriction of low spatial resolution or temperature sensitivity. In this work, we developed a non-contact, in situ temperature measurement approach using a custom micro-Raman spectroscopy platform which has a spatial resolution of 1.5 μm and temperature sensitivity within 0.5 °C. We utilized this method to characterize thin film evaporation from fabricated silicon micropillar arrays. We showed that we can accurately measure the local thin film temperature and map the overall temperature distribution on the structured surfaces at different heat fluxes. We investigated the effects of micropillar array geometries and showed that the temperature rise of the liquid was reduced with the decreasing micropillar pitch due to the increased fraction of the thin film area. This work offers a promising method with micro-Raman to quantify phase change heat transfer on microstructured surfaces. This characterization technique can significantly aid mechanistic understanding and wick structure optimization for various phase-change based thermal management devices.