Nanotip-Induced Boundary Layers to Enhance Flow Boiling in Microchannels

CBET-1336443Li通过潜热蒸发，微通道中的流动沸腾在降低泵浦功率的高工作热通量下实现高温均匀性方面具有巨大潜力，这对于冷却高功率电子和光子学以及提高微型热交换器和反应器的可靠性和能源效率至关重要。然而，微通道中的流动沸腾是随机的，并且受到一些严格的约束，例如气泡限制、粘度和表面张力主导的流动。众所周知，微通道中流动沸腾过程中的传热和传质最终由边界层 (BL) 控制。据观察，通过扰乱BL，例如产生振荡、沿壁引入毛细管流以及促进薄膜蒸发，可以增强微通道中的流动沸腾。然而，通过有意构建和优化 BL 来增强流动沸腾的研究仍然缺乏。本研究通过直接重构或设计BLs，可以在一定程度上根据需要控制和设计微通道内的流动沸腾。这可以通过沿着微通道壁形成创新的亲水性纳米尖端阵列来实现。在通过纳米尖端诱导的 BL 统一多个过渡两相状态后，在该项目中，开发通用的、基于物理的、鲁棒的两相模型将是可行的。同样重要的是，该项目中开发的概念将被积极利用来推动微通道中流动沸腾的极限。该项目的具体任务将致力于实现项目目标：通过开发具有先进轮廓的亲水性纳米尖端阵列来构建和优化BL；实现前所未有的流动沸腾性能；表征微通道中诱导 BL 的新流动沸腾现象；并加深对诱导BLs及其在确定纳米和微米域中两相输运现象中的关键作用的理解。该项目将构成诱导BLs流体力学新研究学科的基础，实现两相输运的新研究方向，并提供有关纳米和微米域两相输运的基本见解。通过控制 BL 大幅增强微通道中的流动沸腾可以更新热/流体领域的两相冷却技术和科学发现。与微电子的兼容性将导致高功率电子和光子学的嵌入式冷却解决方案，这仍然是一项具有挑战性的任务。该项目还将旨在教育下一代微/纳米技术科学家和工程师，并为本科生，特别是代表性不足的少数族裔提供机会，获得微/纳米技术的第一手研究经验，并通过连接最先进的微/纳米技术和基础科学来扩大他们的知识视野。

CBET-1336443LiThrough the latent heat evaporation, flow boiling in microchannels has great potential in achieving high temperature uniformity at a high working heat flux with reduced pumping power, which is critical in cooling high power electronics and photonics and in improving reliability and energy efficiency of micro-heat exchangers and reactors. However, flow boiling in microchannels is stochastic and hampered by several severe constraints such as bubble confinements, viscosity and surface tension force-dominated flows. It is well known that heat and mass transfer are ultimately governed by boundary layers (BLs) during flow boiling in microchannels. It was observed, by disturbing BLs such as creating oscillations, introducing capillary flows along walls, and promoting thin film evaporation, flow boiling in microchannels can be enhanced. However, research to enhance flow boiling by intentionally constructing and optimizing BLs is still lacking. In this study, by directly reconstructing or designing the BLs, the flow boiling in microchannels can be controlled and designed as desired to some extent. This can be achieved by forming innovative hydrophilic nanotip arrays along microchannel walls. After multiple and transitional two-phase regimes are unified by nanotip-induced BLs, in this project, it will be feasible to develop general, physics-based, and robust two-phase models. Equally importantly, the concept developed in this project will be positively utilized to push the limit of flow boiling in microchannels. The specific tasks of this project will be pursued to achieve project goals: construct and optimize BLs by developing hydrophilic nanotip arrays with advanced profiles; achieve an unprecedented flow boiling performance; characterize new flow boiling phenomena with induced BLs in microchannels; and develop understandings of the induced BLs and their critical roles in determining two-phase transport phenomena in nano- and micro-domains.This project will form the basis for a new research discipline in fluid mechanics with induced BLs, enable new research directions in two-phase transport, and provide fundamental insights pertinent to two-phase transport at the nano- and micro-domains. Drastically enhanced flow boiling in microchannels by controlling BLs can update the two-phase cooling technology and scientific discovery in thermal/fluids. Compatibility with microelectronics will lead to embedded cooling solutions for high power electronics and photonics, which is still a challenging task. This project will also aim to educate next generation scientists and engineers in micro/nano-technologies and providing opportunities to undergraduates, in particular underrepresented minorities, to gain first-hand research experience in micro/nanotechnologies and expand their intellectual horizon by bridging the state-of-the-art micro/nanotechnologies and basic science.