BOiliNg flows in SmAll and mIcrochannels (BONSAI): From Fundamentals to Design

盆景是一个雄心勃勃的为期3年的研究项目，旨在研究微型通道中沸腾流动的基本热质传递特征。它将基于空间/时间分辨率诊断的尖端实验与高保真界面分辨率数值模拟相结合，最终为高性能紧凑型蒸发器提供经过验证的热设计工具。拟议的项目汇集了伦敦帝国理工学院、伦敦布鲁内尔大学和诺丁汉大学的研究人员的多学科专业知识，并得到了3家世界领先的研究机构：艾伦·图灵研究所、欧洲核子研究中心(瑞士)和VIR2AL的支持；以及11家行业合作伙伴的支持：Aavid Boyd Thermacore、Alfa Laval、CALGAVIN、Hexag&PIN、HiETA、Hubbard/Daikin、IBM、Oxford NanoSystems、Ricardo、TMD和TTP。微电子行业推动的最近设备小型化的趋势对从数量级cm2去除更高的热负载提出了越来越高的需求。在一些应用中(如制冷)，需要新的“绿色”制冷剂，但由于易燃性或成本原因，需要少量使用，而在其他应用中(如电动汽车和其他应用的电池)，散热不均匀或不稳定对性能和寿命非常不利。多微通道蒸发器中的流动沸腾有望以较低的流体体积满足这种具有挑战性的要求，还可以在远远超出当前最先进水平的系统中实现更好的温度均匀性和更小的泵浦功率。近年来，由于工业(换热)和环境(高效能源利用)的关注，人们对沸腾换热的了解有所提高，主要集中在流型的转变和特征、压降和换热性能方面。然而，我们目前的理解还不足以促进这些微型热交换器在工业中的更广泛使用，这还没有被开发。BONSAI是专门为解决微型设备中沸腾的基本现象及其与工业设计的相关性而量身定做的。需要解决的挑战包括流道形状和表面特性对流动不稳定性、换热和压降的影响，以及液-汽界面随时间的演变、液膜动力学、流场、干汽斑块的出现、热点和局部换热特性之间的关系。将通过理论和新的机器学习方法利用所产生的广泛的实验/数值数据库，以开发基于物理的设计工具，以预测与工业相关的热工水力参数对系统性能的影响。与我们合作伙伴的合作将确保与行业需求保持一致，并加快向行业转移技术。此外，HiETA将提供金属添加剂制造散热器，这些散热器将根据压花技术进行评估，作为批量生产微通道热交换器的方式；牛津纳米系统公司将提供纳米结构表面涂层；IBM将支持访问其研究实验室，重点关注数值求解器和横向扩展研究的高效并行。拟议的研究不仅将使两相热解决方案得到更广泛的采用，从而满足工业部门当前和未来的需求，而且还将导致数据中心更高效的热管理，相关减少能源消耗和碳足迹，以及回收和重新利用目前被拒绝的废热。这将构成英国在2050年前实现排放目标的重要一步。此外，盆景将与EPSRC繁荣成果交付计划2016-2020年相结合，并推动与制造未来主题相关的技术进步，为建设一个富有生产力和韧性的国家做出贡献。

BONSAI is an ambitious 3-year research project aimed at investigating the fundamental heat and mass transfer features of boiling flows in miniaturised channels. It combines cutting-edge experiments based on space/time-resolved diagnostics, with high-fidelity interface-resolving numerical simulations, to ultimately provide validated thermal-design tools for high-performance compact evaporators. The proposed project assembles multidisciplinary expertise of investigators at Imperial College London, Brunel University London, and the University of Nottingham, with support from 3 world-leading research institutes: Alan Turing Institute, CERN (Switzerland) and VIR2AL; and 11 industry partners: Aavid Boyd Thermacore, Alfa Laval, CALGAVIN, HEXAG&PIN, HiETA, Hubbard/Daikin, IBM, Oxford nanoSystems, Ricardo, TMD and TTP.The recent trend towards device miniaturisation driven by the microelectronics industry has placed an increasing demand on removing higher thermal loads, of order of MW/m2, from areas of order cm2. In some applications (e.g. refrigeration) new 'green' refrigerants are needed, but in small volumes due to flammability or cost, while in others (e.g. batteries for EV and other applications) non-uniform or unsteady heat dissipation is highly detrimental to performance and lifetime. Flow boiling in multi-microchannel evaporators promises to meet such challenging requirements with low fluid volumes, also allowing better temperature uniformity and smaller pumping power, in systems that go well beyond the current state-of-the-art. Due to significant industrial (heat exchange) and environmental (efficient energy use) interest, the understanding of boiling heat transfer has improved in recent years, with focus on flow pattern transitions and characteristics, pressure drop, and heat transfer performance. However, our current understanding is simply insufficient to facilitate the wider use of these micro-heat-exchangers in industry, which remains unexploited.BONSAI has been tailored specifically to address the fundamental phenomena underlying boiling in miniaturised devices and their relevance to industrial design. The challenges to be addressed include the impact of channel shape and surface characteristics on flow instabilities, heat transfer and pressure drop, and the relationship between the time-dependent evolution of the liquid-vapour interface, thin liquid-film dynamics, flow field, appearance of dry vapour patches, hot spots, and local heat transfer characteristics. The extensive experimental/numerical database generated will be exploited via theoretical and novel machine-learning methods to develop physics-based design tools for predicting the effects of industrially-relevant thermohydraulic parameters on system performance. The collaboration with our partners will ensure alignment with industrial needs and accelerate technology transfer to industry. In addition, HiETA will provide Metal Additive Manufacturing heat sinks that will be assessed against embossing technologies as ways of mass-producing microchannel heat exchangers, Oxford nanoSystems will provide nano-structured surface coatings, and IBM will support visits to their Research Labs focussed on efficient parallelisation of the numerical solver and scale-out studies.The proposed research will not only enable a wider adoption of two-phase thermal solutions and hence the meeting of current and future needs across industrial sectors, but also will lead to more efficient thermal management of data-centres with associated reduction in energy consumption and carbon footprint, and the recovery and reuse of waste heat that is currently being rejected. This will constitute an important step towards meeting the UK's emission targets by 2050. Additionally, BONSAI will integrate with EPSRC Prosperity Outcomes of Delivery Plan 2016-20 and enable technological advances in relation to the Manufacturing the Future theme, contributing to a Productive and Resilient Nation.