A Wettability-Mediated Microdroplet Under Electrowetting Effect for Hotspot Cooling

This work reports an experimental investigation of electrowetting (EW)-driven microdroplets for on-chip hotspot cooling applications. A discrete microdroplet of deionized (DI) water with 4
-
${\mu }\text {l}$
volume is transported over an electrode array in a single-plate EW device. The instantaneous shape of the droplet and its wetting behavior during the two-phase heat dissipation process have been analyzed for different operating conditions. In conventional EW devices, the cooling of a hydrophobic hotspot by a microdroplet exhibits evaporation with low contact line pinning, and the droplet skitters away from the hotspot, resulting in underperformance of the device. In this work, we have introduced a super hydrophilic surface using an anodization technique to improve the heat dissipation capacity of an EW device. The droplet eventually wets the hydrophilic hotspot and maintains a relatively large surface area with low thermal resistance, enhancing heat dissipation capacity. A maximum 210.7% enhancement in heat transfer efficiency of a coolant droplet over a superhydrophilic hotspot is observed compared to that on the hydrophobic surface. Furthermore, continuous droplet feeding has been applied over the hydrophilic surface to tackle the quick evaporation of the droplet. The coalescence of two successive droplets produces extra cooling effects on the hotspot.