Capillary Transport Enhancement in Hybrid Micropillar Wicks Fabricated with UV-Laser Ablation

Passive cooling devices like heat pipes and vapor chambers utilize a capillary-driven liquid–vapor phase change loop to spread extreme heat flux from localized hotspots in microprocessors. Their performance is often limited by capillary transport mechanisms, which dictate fluid routing through their internal wick structures. This study presents a simple technique to create rough, hierarchical pin-fin microstructure arrays using a UV-laser cutter and compares transport rates in these hybrid wicks against analogously shaped, plasma-etched, smooth surfaces to investigate enhanced capillary action. One-dimensional capillary wicking experiments demonstrate increased rates of capillary filling, up to 117%, and two models are developed to evaluate these results. An empirical power-law-based model connects the magnitude of wicking enhancement to the aspect ratio and nondimensional interpillar gap of each wick design, predicting increased transport rates between sample types with an 8% error. A simple naïve force enhancement model derived from first principles prescribes a roughness factor that predicts the change in wicking rates with a 10% error. Though neither model captures the outlier behavior observed in exceptional aspect ratios─ tall, densely packed pillars or short, widely spaced patterns─divergent flow mechanisms are delineated beyond 1 < AR < 6, and roughness effects on capillary flow are herein reported as a starting point for further fundamental studies.