NDLI: Spot Cooling Using Electrowetting-Controlled Thin Film Heat Transfer

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Cheng, Jiangtao Chen, Chung-Lung
Copyright Year	2012
Abstract	We report an electrowetting-controlled cooling system with site-specific treatments on the heat source (evaporator or hot spot) surfaces. Electrowetting-on-dielectric (EWOD) has great potential in thermal management because EWOD-driven droplet transport has unique characteristics of prompt response, low power consumption and programmable paths without the need for any mechanical moving parts. Prompt and fast droplet transport is necessary for adaptive and active cooling of high heat flux targets. Using a multi-channel DC/AC control system, we carried out sequenced activation of AC voltages on coplanar electrodes and transmitted a droplet to the spot target along a programmable path. With high positioning accuracy at the chip level, we have successfully transmitted a water droplet of 15 μL at speeds as high as ∼10 cm/s. We further improved electrowetting cooling performance by coating a fine copper screen on the cooling targets. The capillarity associated with the copper screen facilitates the delivered droplets automatically spreading and clinging to the target surfaces. As a result, heat transfer is in the more efficient form of filmwise evaporation at the evaporator sites. To maintain a thin film with proper thickness on the hot spots, we implemented EWOD-assisted droplet splitting and merging to precisely control the droplet volume to avoid fluid flooding (accumulation) on the hot spot surfaces. Our investigation indicates that thin-film evaporation is a high-efficiency heat transfer mechanism on a hydrophilized hot spot surface. Based on EWOD technique with surface treatments, the superheat on a hot spot of 4mm × 4mm was maintained well below 30°C even when the heat flux reached as high as 80W/cm2. The closed loop of this novel thermal management system can potentially function as a wickless vapor chamber or heat pipe with enhanced heat dissipation capabilities.
Sponsorship	Nanotechnology Institute
Starting Page	275
Ending Page	281
Page Count	7
File Format	PDF
ISBN	9780791854778
DOI	10.1115/MNHMT2012-75032
Conference Proceedings	ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer
Language	English
Publisher Date	2012-03-03
Publisher Place	Atlanta, Georgia, USA
Access Restriction	Subscribed
Subject Keyword	Water Energy consumption Cooling Vapors Control systems Cooling systems Evaporation Coatings Floods Surface finishing Heat flux Thin films Electrodes Heat Fluids Capillarity Energy dissipation Heat pipes Drops Thermal management Coating processes Copper Heat transfer
Content Type	Text
Resource Type	Article

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