Demonstration of hotspot cooling using digital microfluidic device

Abstract

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.

Materials and Manufacturing Methods for EWOD Devices: Current Status and Sustainability Challenges

“…One of the most studied case is the cooling of surfaces by droplets of coolants on demand. [ 120–123 ] Ahmad et al. designed a method for cooling hot spots in electronic devices.…”

Advances in Microscale Droplet Generation and Manipulation

“…The precise generation and manipulation of small droplets remain attractive due to their applications in many domains. The generation of these droplets is of significant interest in the fields of aerosol formation, , chemistry for performing chemical reactions, , micro/nanoparticle synthesis, , thermal management for cooling electronic devices, , and pathogen carriers in biology. , However, the generation and manipulation of droplets less than the capillary length scale always remain challenging. This is because of the domination of surface tension force at such a length scale, which limits the droplet size .…”

Effects of Liquid Viscosity on the Formation and Attenuation of Capillary Waves Induced by AC Electrowetting-on-Dielectric

“…When an electrostatic force is applied to the three-phase contact line, , the contact line is displacedthis displacement is the origin of EWOD. This phenomenon has inspired the rapid development of diverse applications. − For example, the asymmetric wetting-induced droplet movement on a planar EWOD device with patterned electrodes enables the booming of digital microfluidics for chemical and biomedical applications. − Furthermore, the EWOD configuration in an oil/aqueous interface has been widely employed in the development of focal-length-tunable lenses − and advanced display technologies. − In recent years, EWOD has been expanded to a free air/aqueous interface with an AC electric signal. The variation of wettability in EWOD devices drives sessile droplet oscillations − or continuous surface contact line variations, − inducing the formation of capillary waves.…”