Demonstration of hotspot cooling using digital microfluidic device

To respond to the dire need of smaller but more effective ways to handle non-uniform temperature distribution (a.k.a. hotspots) within an electronic device, this paper presents the concept of droplet-based cooling and its proof-of-concept demonstration. An electrowetting-on-dielectric (EWOD) digital microfluidic device with parallel plates configuration was used to control coolant droplet motion. Periodic rise and falls in hotspot temperature were measured when multiple water droplets moved over the hotspot surface while a constant heat flux was applied at the hotspot. Synchronized high-speed video data of droplet motion shows that phase-change heat transfer (i.e. evaporation) at the water droplet meniscus coincided with additional temperature drop at the hotspot. Furthermore, the heat transfer coefficient of water droplet evaporation was measured on a hydrophilic hotspot surface. The hydrophilic surface regulated the hotspot temperature within a lower envelope for a longer time.