Graduation Semester and Year

2018

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Hyejin Moon

Abstract

The increased use of smart devices and great strides in fabrication technologies have resulted in densely packed electronics. Combined with 3D packaging, high heat uxes have become the norm. The need for advanced thermal management solutions has risen. Most devices based on their load pro le and architecture are susceptible to non-uniformities in heat uxes. These non-uniformities with very high heat uxes are known as hotspots. Mitigation of hotspots is very important for the normal functioning and long term reliability of microprocessors. Multiple attempts have been made at developing microscale thermal solutions. Most prominent among them are microchannels and heat pipes. The shrinking size of electronics demands compact thermal solutions. One of them is electrowetting on dielectric (EWOD) digital micro uidics. They are highly suitable due to their unique features such as no moving mechanical parts, low power consumption and pump-less operation. Moreover, unlike microchannels, they are immune to ow instabilities. This research focuses on utilizing EWOD devices to cool hotspots evaporatively. Indium tin oxide (ITO) as well as nickel thin lm resistors are integrated in the devices to simulate hotspots as well as make temperature measurements. The experiments were carried out in ambient conditions. Cooling of the hotspot is studied by measuring the hotspot temperature with di erent heat uxes and water droplet delivery speeds. Heat uxes higher than 40 W/cm2 resulted in enhanced cooling due to phase change happening at the advancing and receding menisci of droplets. Sustained droplet motion cools and maintains the hotspot temperature. vi Phase change phenomena although present at high heat uxes, was not the main mode of heat transfer. To increase the role of evaporation, a superhydrophilic area was integrated in the electrowetting device. The superhydrophilic region, owing to its near zero contact angle, increases the length of the transition region in the thin lm[1]. Visuals of spreading of the liquid thin lm synchronized with the hotspot temperature data was used to study evaporative hotspot cooling. Di erent spreading regimes were observed corresponding to various heat transfer modes governing heat dissipation.Also, a thermal resistance analysis was conducted to understand the heat transfer mechanism. The e ect of various evaporation parameters was studied. The work focuses on studying evaporative heat transfer in hotspot cooling. While doing so, it also elucidates the challenges faced in designing a purely evaporative hotspot cooling solution.

Keywords

Electronics cooling, Microfluidics, Electrowetting, Phase change

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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