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

Abstract

Capillary-driven 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), a 160–500- $\mu $ m-wide bridge $\mu $ -cooler. To area scale such a $\mu $ -cooler, a silicon-based 3-D manifold is a promising option due to fine microchannel features that enable capillary wicking over longer distances. This study presents design optimization, performance data, and modeling results for capillary-based $\mu $ -coolers with a silicon 3-D manifold. By varying the vapor extraction pathways spacing (80, 200, 400, 600, 800 $\mu $ m) between liquid delivery microchannels, we show the impact of effective wicking length on thermal performance. The 3-D manifold with 400- $\mu $ m vapor spacing achieves the best overall performance: critical heat flux (CHF) of up to 580 Wcm^–2 with a low superheat of $5.4~^{\circ }$ C, yielding a thermal resistance less than 0.01 cm²KW⁻¹ with a very small flow rate of 3.37 gmin⁻¹. This optimized geometry maximizes active boiling area while maintaining sufficient capillary-driven liquid replenishment. Too-small spacing leads to flooding and a reduction in effective area available for two-phase boiling, while too-large spacing limits lateral liquid transport and causes dry out. The experimental results validate the area-scaling model and confirm its effectiveness as a design tool for a large-area cooler.