CAREER: Fundamental Transport Mechanisms of Evaporation From Non-Axisymmetric Droplets Confined on Hollow Micropillars Structures

微电子和电力电子技术的进步彻底改变了人们工作、交流和生活的方式。然而，小型化和高功率密度需要增强的冷却技术来可靠运行。两相液体冷却，如微尺度液滴的直接蒸发，利用汽化的高潜热来有效散热。非球形液滴的蒸发，由于其更大的表面积和半月板曲率，与球形液滴相比，表现出非常不同的蒸发速率。因此，可以通过使用微工程表面来控制液滴形状来提高冷却速度。该项目将为两相冷却技术的突破奠定理论和实验基础，从而释放用于数据中心、电动汽车和人工智能的下一代电子产品的全部潜力。CAREER项目的长期教育目标是将基于项目的研究成果整合到教育模块中，并通过吸引高中到研究生阶段的学生参与表面工程和热输运研究，激励STEM专业的学生。本项目旨在确定在非轴对称微滴蒸发过程中的不同传热传质模式。近百年来，人们对无底液滴的蒸发现象进行了广泛的研究，但大多数研究都集中在有顶球形液滴的蒸发上。因此，非轴对称液滴形状如何影响不同的蒸发机制以及微工程结构如何控制液滴几何形状仍不清楚。本项目旨在阐明微工程结构的几何形状和尺寸如何影响非轴对称微液滴蒸发的接触线动力学、热毛细流动、界面传输和蒸汽扩散特性。新的实验方法将基于压力控制的微流体系统、微粒子图像测速和平面激光诱导荧光成像来量化蒸发质量输运并捕获局部流量和温度模式。这些方法将推进热流体领域的实验技术，用于探测液-气两相系统的输运机制，为非轴对称微液滴蒸发过程中的液-气界面质量输运、微对流和蒸汽扩散提供见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Technology advances in micro- and power-electronics have revolutionized the way people work, communicate, and live. However, the miniaturization and high power densities require enhanced cooling technologies for reliable operation. Two-phase liquid cooling, such as direct evaporation from microscale droplets, utilizes the high latent heat of vaporization to effectively dissipate heat. Evaporation from non-spherical droplets, owing to their larger surface area and meniscus curvature, exhibits very different evaporation rates compared to a spherical droplet. Consequently, cooling rates can be enhanced by using micro-engineered surfaces to control droplet shapes. This project will establish a theoretical and experimental basis for breakthroughs in two-phase cooling technologies that can unleash the full potential of next-generation electronics used for data centers, electric vehicles, and artificial intelligence. The long-term educational goal of this CAREER project is to integrate project-based research outcomes into education modules and motivate STEM majors by engaging students from high school to the graduate level in surface engineering and thermal transport research. This project seeks to identify the different modes of heat and mass transfer during the evaporation of non-axisymmetric microdroplets. While sessile droplet evaporation has been studied extensively over the past hundred years, most of them have only focused on the evaporation of droplets with capped spherical shapes. Consequently, how different evaporation mechanisms are affected by the non-axisymmetric droplet shape and how the droplet geometry is controlled by micro-engineered structures remain unclear. This project seeks to elucidate how the geometry and dimensions of micro-engineered structures affect the contact line dynamics, thermocapillary flow, interfacial transport, and vapor diffusion characteristics for evaporating non-axisymmetric microdroplets. Novel experimental methods will be utilized based on a pressure-controlled microfluidic system, micro-particle image velocimetry, and planar laser induced fluorescence imaging to quantify evaporation mass transport and capture the local flow and temperature patterns. These approaches will advance experimental techniques in thermofluidic fields for probing the transport mechanisms of liquid-vapor two-phase systems, providing insights into liquid-vapor interfacial mass transport, micro-convection, and vapor diffusion during evaporation of non-axisymmetric microdroplets.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.