Nanotip-Induced Boundary Layers to Enhance Flow Boiling in Microchannels

CBET-1336443Li通过潜热蒸发，微通道内的流动沸腾具有在较高的工作热流密度下以较低的泵浦功率获得高温均匀度的巨大潜力，这对于冷却大功率电子产品和光电子产品，提高微型换热器和反应堆的可靠性和能效是至关重要的。然而，微通道内的流动沸腾是随机的，并受到气泡约束、粘度和表面张力主导流动等严重约束的阻碍。众所周知，微通道内流动沸腾过程中的传热传质最终由边界层控制。观察到，通过扰动边界层，如产生振荡、沿壁面引入毛细管流、促进薄膜蒸发等，可以增强微通道内的流动沸腾。然而，通过有意识地构建和优化流动沸腾来强化流动沸腾的研究还很缺乏。在本研究中，通过直接对BLS进行改造或设计，可以在一定程度上实现对微通道内流动沸腾的控制和设计。这可以通过沿微通道壁形成创新的亲水性纳米尖端阵列来实现。在此项目中，通过纳米针尖诱导的BLS来统一多个和过渡性的两相区域之后，将有可能开发出通用的、基于物理的和健壮的两相模型。同样重要的是，本项目中提出的概念将被积极地用于推动微通道内流动沸腾的极限。这个项目的具体任务是为了实现项目目标：通过开发具有先进轮廓的亲水性纳米针尖阵列来构建和优化边界层；实现前所未有的流动沸腾性能；利用微通道中的诱导边界层来表征新的流动沸腾现象；以及加深对诱导边界层及其在决定纳米和微域两相传输现象中的关键作用的理解。本项目将为建立具有诱导边界层的流体力学的新的研究学科奠定基础，使两相传输的新的研究方向成为可能，并提供与纳米和微域的两相传输相关的基本见解。通过控制气液两相流来强化微通道内的流动沸腾，可以更新两相冷却技术和热/流体方面的科学发现。与微电子的兼容性将导致高功率电子和光电子的嵌入式冷却解决方案，这仍然是一项具有挑战性的任务。该项目还将致力于在微纳技术方面教育下一代科学家和工程师，并为本科生，特别是未被充分代表的少数群体提供机会，通过将最先进的微纳技术与基础科学联系起来，获得微纳技术方面的第一手研究经验，并扩大他们的智力视野。

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.