Drop Evaporation on Rough Hot-Spots: Effect of Wetting Modes

Hot-spots are a common occurrence in power electronics which become increasingly hotter as chips become denser. Novel cooling technologies are emerging to cope with this increasing heat load, which imbed a condenser to supply cooling drops to the evaporator resting on the hot-spots. Nonetheless, the evaporation process of the drops has been overlooked. Here, we conducted a series of experiments to understand how the evaporation and motion of drops are influenced by the wetting mode of rough hot-spots. We fabricated three different surfaces exhibiting full (Wenzel) or partial (Cassie-Baxter) wetting and the hot-spot is imposed by laser irradiation. We report a direct link between drop motion and wetting mode with the partial wetting drops being highly mobile, attributable to lower pinning energy based on an energy analysis. This study provides a framework for future modifications in hot-spot cooling to account for drop motion which should greatly influence the overall heat removal performance.