Experimental Optimization of Liquid-Vapor Phase Separation in High Heat Flux Capillary-Driven μ-Coolers

Capillary-drive two-phase cooling offers an effective and energy-efficient solution for high-heat-flux thermal management in compact electronic systems. To enhance boiling performance, it is critical to separate the liquid supply and vapor escape pathways. Prior work has demonstrated liquid-vapor phase separation in copper inverse opals (CuIOs) 160 um to 500 um wide bridge μ-cooler. To area scale such μ-cooler, silicon-based 3D manifold is a promising option due to fine microchannel feature that enables capillary wicking over longer distances . This study presents design optimization, performance data and modeling results for capillary-based μ-coolers with silicon 3D manifold. By varying the vapor extraction pathways spacing (80, 200, 400, 600, 800 μm) between liquid delivery microchannels, we show the impact of effective wicking length on thermal performance. The 3D manifold with 400μm vapor spacing achieves the best overall performance: critical heat flux of up to 580Wcm-² with a low superheat of 5.4°C, yielding a thermal resistance less than 0.01 cm²KW^-1 with a very small flow rate of 3.37gmin^-1. This optimized geometry maximizes active boiling area while maintaining sufficient capillary-driven liquid replenishment. Too-small spacing leads to flooding and reduction in effective area available or two-phase boiling while too-large spacing limits lateral liquid transport and causes dryout. The experimental results validate the area-scaling model and confirm its effectiveness as a design tool for large-area cooler.