Nanotip-Induced Boundary Layers to Enhance Flow Boiling in Microchannels

通过潜热蒸发，微通道内的流动沸腾在低泵浦功率下以高工作热流密度实现高温度均匀性方面具有很大的潜力，这对于大功率电子器件和光子学的冷却以及提高微热交换器和反应器的可靠性和能效至关重要。然而，微通道中的流动沸腾是随机的，并且受到气泡限制、粘度和表面张力主导的流动等一些严重约束的阻碍。众所周知，在微通道流动沸腾过程中，传热传质最终是由边界层（BLs）控制的。结果表明，通过对微通道进行扰动，如产生振荡、引入毛细管沿壁流动、促进薄膜蒸发等，可以增强微通道内的流动沸腾。然而，通过有意构建和优化BLs来提高流动沸腾的研究仍然缺乏。在本研究中，通过直接重构或设计BLs，可以在一定程度上控制和设计微通道内的流动沸腾。这可以通过沿着微通道壁形成创新的亲水纳米尖端阵列来实现。在纳米尖端诱导的双相物质统一了多相和过渡两相体系之后，本项目将有可能开发出通用的、基于物理的、健壮的两相模型。同样重要的是，本项目开发的概念将被积极地用于推动微通道中流动沸腾的极限。本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BLs；实现前所未有的流动沸腾性能；表征微通道中诱导bl的新型流动沸腾现象；并发展对诱导bl及其在决定纳米和微域两相输运现象中的关键作用的理解。该项目将为诱导bl流体力学的一个新的研究学科奠定基础，为两相输运的研究开辟新的方向，并为两相输运在纳米和微领域的研究提供基础性的见解。通过控制BLs来大幅提高微通道内的流动沸腾，可以更新两相冷却技术和热/流体科学发现。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。该项目还旨在培养下一代微纳米技术的科学家和工程师，并为本科生，特别是少数族裔提供机会，通过连接最先进的微纳米技术和基础科学，获得微纳米技术的第一手研究经验，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.