Enhanced Multiscale Boiling Surfaces (EMBOSS): From Fundamentals to Design

沸腾现象是许多行业中加热和冷却任务的核心，例如冷却和制冷、发电和化工制造。沸腾换热的限制是由于高热流密度下的表面干燥，导致换热表面上的局部热点和更大的设备要求。虽然这对许多行业来说是一个严重的问题，但在处理小规模系统时，这就更是一个问题，例如用于微电子冷却的系统，在这些系统中，如果不能有效地散热，会导致局部过热和部件的潜在损坏。这种系统在空间上不均匀、不稳定的耗散热的产生不利于它们的性能和寿命。有效换热器面积为Sq量级。Cm，其热流密度约为MW/平方米。这需要一种变革性的、阶梯式的变化，超越目前最先进的在局部“热点”冷却2-15 mW/平方米的热流以防止烧毁。已经进行了一些尝试，通过改变表面特性来扩展热流的上限，目的是改善汽泡的成核、气泡的脱离以及随后液体对表面的再润湿。尽管取得了进展，但以前关于池-(和潜在的流动-)沸腾表面的工作并没有涉及到开发最佳表面形貌的合理方法。例如，核态沸腾换热(NBHT)随着润湿性的增加而降低，设计人员必须考虑与表面结构和流体相行为相关的成核点密度、相关气泡偏离直径和频率。对于较高的表面润湿性，较小尺度的表面结构特征(例如空穴)可以作为成核点；对于较低的润湿性，空穴的尺寸而不是其拓扑结构将起主导作用。因此，仅用粗糙度来表征表面不足以解释沸腾曲线的变化：必须详细研究流体-表面耦合以增强NBHT和临界热流密度。EMBOSS汇集了来自布鲁内尔、爱丁堡和帝国理工学院的多学科研究人员团队，以及六个行业合作伙伴和一名合作者(Aavid Thermacore、TMD Ltd、牛津纳米系统、Intrinsiq Material、Alfa Laval、CALGAVIN和OxfordLaser)，他们在尖端微制造、实验技术以及分子、介观和连续尺度建模和模拟方面拥有专业知识。EMBOSS框架将为池沸腾热管理系统的操作原型的合理设计、制造和优化提供信息。设计的最佳性将从材料和能源的节约、热交换设备的效率和占地面积、排放的减少和工艺的可持续性来衡量。与我们的合作伙伴的合作将确保与行业需求保持一致，并将加快技术向行业的转移。这些伙伴将通过项目进展会议提供指导和咨询意见，其中一些伙伴还将主持会议。此外，Alfa Laval将为实验工作提供铜焊换热器作为冷凝器，Intrinsiq将为涂层表面提供铜墨，牛津纳米系统公司将提供纳米结构表面涂层。该项目将整合EPSRC繁荣成果和产业战略挑战基金在能源(Resilient Nation)、制造业和数字技术(Resilient Nation，Productive Nation)领域确定的挑战，作为推动经济增长的领域。

Boiling phenomena are central to heating and cooling duties in many industries, such as cooling and refrigeration, power generation, and chemical manufacture. Limitations to boiling heat transfer arise through surface dry-out at high heat flux, leading to localised hot-spots on heat transfer surfaces and larger equipment requirements. Whilst this is a significant problem for many industries, it becomes even more of an issue when dealing with small-scale systems, such as those used for cooling of microelectronics, where failure to remove heat effectively leads to localised overheating and potential damage of components. Spatially non-uniform and unsteady dissipative heat generation in such systems is detrimental to their performance and longevity. The effective heat exchanger area is of order sq. cm, with heat fluxes of order MW/sqm. This requires a transformative, step-change, beyond the current state-of-the-art for cooling heat fluxes between 2-15 MW/sqm at local "hot spots" to prevent burn out.A number of attempts have already been made to extend the upper boundary for the heat flux through alteration of surface characteristics with the aim of improved nucleation of vapour bubbles, bubble detachment, and subsequent rewetting of the surface by liquid. Despite the progress made, previous work on surfaces for pool- (and potentially flow-) boiling does not involve a rational approach for developing optimal surface topography. For instance, nucleate boiling heat transfer (NBHT) decreases with increasing wettability, and the designer must consider the nucleation site density, associated bubble departure diameter, and frequency related to the surface structure and fluid phase behaviour. For high surface wettability, the smaller-scale surface structure characteristics (e.g. cavities) can act as nucleation sites; for low wettability, the cavity dimensions, rather than its topology, will dominate. Therefore, characterising surfaces in terms of roughness values is insufficient to account for the changes in the boiling curve: the fluid-surface coupling must be studied in detail for the enhancement of NBHT and the critical heat flux.EMBOSS brings together a multi-disciplinary team of researchers from Brunel, Edinburgh, and Imperial, and six industrial partners and a collaborator (Aavid Thermacore, TMD ltd, Oxford Nanosystems, Intrinsiq Materials, Alfa Laval, CALGAVIN, and OxfordLasers) with expertise in cutting-edge micro-fabrication, experimental techniques, and molecular-, meso- and continuum-scale modelling and simulation. The EMBOSS framework will inform the rational design, fabrication, and optimisation of operational prototypes of a pool-boiling thermal management system. Design optimality will be measured in terms of materials and energy savings, heat-exchange equipment efficiency and footprint, reduction of emissions, and process sustainability. The collaboration with our partners will ensure alignment with the industrial needs, and will accelerate technology transfer to industry. These partners will provide guidance and advice through the project progress meetings, which some of them will also host. In addition, Alfa Laval will provide brazed heat exchangers as condensers for the experimental work, Intrinsiq will provide copper ink for coating surfaces and Oxford nanoSystems will provide nano-structured surface coatings. The project will integrate the challenges identified by EPSRC Prosperity Outcomes and the Industrial Strategy Challenge Fund in Energy (Resilient Nation), manufacturing and digital technologies (Resilient Nation, Productive Nation), as areas to drive economic growth.