Optimization and thermal characterization of uniform silicon micropillar based evaporators

The development of high power density and compact electronic devices result in the generation of large and concentrated heat loads, which need to be dissipated effectively to avoid electronics failure. Vapor chambers are promising candidates to overcome the thermal management challenges, owing to its passive working mechanism and excellent heat removal capability. Micropillar-based evaporators for these vapor chambers allow for high capillary pressure, large permeability and extended evaporation areas, which enhances the critical dryout heat flux of the vapor chamber. However, predictive models that evaluate the performance of micropillar evaporators are limited, where the selection of micropillar geometries is typically based on empirical data and the evaporator temperature rise has not been considered. In this paper, we report a comprehensive and systematic study of cylindrical silicon micropillar-based uniform evaporators. First, we constructed a semi-analytical model to predict the capillary-limited dryout heat flux. We performed an optimization to select the micropillar geometries by considering the evaporator temperature rise. Subsequently, we microfabricated uniform evaporators with various geometries and thermally characterized the evaporators in a controlled vacuum environmental chamber. Then, we validated the model with the experimental results and showed that the model and experiments have reasonable agreement within 20%. The heat transfer coefficients decreased with smaller micropillar diameter/pitch ratios and taller micropillar heights. This work provides comprehensive insights into the design of uniform micropillar-based evaporators and can serve as useful guidelines for advanced vapor chambers and other phase-change devices.