This item is under embargo and not available online per the author's request. For access information, please visit http://libanswers.wustl.edu/faq/5640.

Date of Award

Spring 5-2021

Author's School

McKelvey School of Engineering

Author's Department

Mechanical Engineering & Materials Science

Degree Name

Master of Science (MS)

Degree Type

Thesis

Abstract

With the increasing demand for higher-performance chips, the architecture of these semiconductor devices becomes more complex, leading to the need for higher-performance cooling technologies. For example, 3D stacked chips offer several advantages, including mixed functionality, reduced signal delay, and a smaller footprint. However, these devices yield higher heat densities due to the heat compounded from one stacked die to the next. While traditional single-phase cooling technologies can dissipate large heat fluxes, its performance is inversely proportional to its hydraulic diameter leading to larger required pumping powers. Two-phase cooling is a promising technique for dissipating high heat fluxes by utilizing the large latent heat of vaporization associated with the phase change process. This study focuses on the evaporation of pinned droplets, whose high perimeter-to-area ratio provides a high heat transfer coefficient per unit area. In particular, a triangular asymmetric droplet has proved to be the optimal shape for evaporative heat transfer based on the perimeter-to-area ratio criterion. Beyond optimizing the shape of the droplet, another approach to increasing the perimeter-to-area ratio is to increase the number of droplets per unit area while decreasing the size of each droplet. Although a few studies have explored this approach, none of them have utilized asymmetric droplets. However, it is known that the vapor diffusion confinement effect negatively influences the evaporation of droplets. Hence, both the size of the droplets and the distance between them have lower limits. In this study, we create a patterned array of micropillars with droplets pinned on top, where the shape of the micropillars constrains the shape of the droplets. Using pattern simplification and the Particle Swarm Optimization algorithm, we find an optimized micropillar array structure for asymmetric droplet evaporation. Compared with an orthogonal arrangement, a staggered arrangement shows a 14.1% increase in heat transfer performance under constant heat flux compared with a circular orthogonal micropillar array. In addition to providing better heat transfer performance, this optimization study also provides a better understanding of the confinement effect between neighboring asymmetric droplets.

Language

English (en)

Chair

Professor Damena Agonafer

Committee Members

Professor David Peters Professor Ramesh Agarwal

Available for download on Tuesday, April 25, 2023

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