Date of Award
Master of Science (MS)
Enhanced Heat Transfer Performance by Shape Optimization of a Non-axisymmetric Droplet Evaporating on a Heated Micropillar
Department of Mechanical Engineering and Materials Science
Washington University in St. Louis, 2019
Research Advisor: Professor Damena Agonafer
The stacked multilayer 3D IC structure used in next generation high-powered electronics poses great challenges in dissipating their large heat flux, which causes extreme difficulties for traditional cooling technologies. In response, more advanced two-phase liquid cooling technologies, such as droplet evaporation, which utilizes the latent heat of vaporization to remove excessive heat, have been widely investigated. Compared to traditional single-phase cooling techniques, two-phase cooling based on droplet evaporation offers both high efficiency and an exceptionally high heat dissipation rate. Compared to a spherical droplet, a non-spherical droplet on a non-axisymmetric pillar, with its different perimeter-to-area ratio and meniscus curvature, exhibits very different interfacial mass transport features. In particular, the higher ratio of the perimeter length to the solid-liquid area provides a relatively larger thin film region and therefore a smaller thermal resistance, while the high local curvature facilitates a stronger local vapor diffusion rate. However, the optimal pillar shape is still uncertain. In this study, using the Particle Swarm Optimization algorithm, we develop a shape optimization tool for max non-axisymmetric droplet evaporation on a micropillar structure. The optimization tool integrates the algorithm calculation and curve generation in Matlab, the droplet shape generation in Surface Evolver, the geometry evolution in Solidworks, and the evaporation simulation in COMSOL. The optimized micropillar shape shows a 9% improvement in the heat transfer coefficient for the same liquid-vapor interfacial area and the same substrate area. Comparative evaporation experiments using fabricated micropillar samples with a baseline triangular pillar shape, validate the simulation results, with a relative error of less than 9.7% in evaporation rate.
Damena Agonafer David Peters Ramesh Agarwal