Nanotip-Induced Boundary Layers to Enhance Flow Boiling in Microchannels

通过潜热蒸发，微通道中的流动沸腾在以降低的泵送功率在高工作热通量下实现高温均匀性方面具有巨大的潜力，这在冷却高功率电子器件和光子器件以及提高微型热交换器和反应器的可靠性和能量效率方面至关重要。然而，微通道内的流动沸腾是随机的，并受到几个严重的限制，如气泡约束，粘度和表面张力力占主导地位的流动。微通道内流动沸腾传热传质的最终控制因素是边界层。研究发现，通过扰动边界层，如产生振荡、沿壁面沿着引入毛细流动和促进薄膜蒸发，可以增强微通道内的流动沸腾。然而，通过有意地构建和优化BL来增强流动沸腾的研究仍然缺乏。在本研究中，通过直接改造或设计边界层，可以在一定程度上控制和设计微通道内的流动沸腾。这可以通过沿沿着微通道壁形成创新的亲水性纳米尖端阵列来实现。在多个和过渡两相制度统一的纳米尖诱导的BL，在这个项目中，它将是可行的，开发通用的，基于物理的，和强大的两相模型。同样重要的是，在这个项目中开发的概念将被积极利用，推动微通道中的流动沸腾的极限。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;并发展的诱导BL及其在确定纳米和微米两相传输现象的关键作用的理解，该项目将形成具有诱导BL的流体力学新研究学科的基础，使两相运输的新研究方向成为可能，并提供与纳米和微米领域的两相运输相关的基本见解。通过控制边界层来强化微通道内的流动沸腾，可以促进两相冷却技术的发展和热/流体领域的科学发现。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。该项目还旨在教育下一代科学家和工程师掌握微/纳米技术，并为本科生，特别是代表性不足的少数群体提供机会，以获得微/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.