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

在许多工业中，沸腾现象是加热和冷却的核心，如冷却和制冷、发电和化学制造。在高热流密度下，表面干燥会导致沸水传热的局限性，从而导致传热表面出现局部热点和对设备的要求更大。虽然这对许多行业来说都是一个重大问题，但在处理小型系统（例如用于微电子冷却的系统）时，它变得更加严重，因为无法有效地散热会导致局部过热和组件的潜在损坏。这种系统的空间不均匀和不稳定的耗散热产生不利于其性能和寿命。有效热交换器面积为5平方。cm，热流密度为毫瓦/平方米。这需要一种变革性的、阶梯式的改变，超越目前最先进的冷却热通量在2-15兆瓦/平方米之间的局部“热点”，以防止烧毁。已经进行了许多尝试，通过改变表面特性来扩大热通量的上边界，目的是改善蒸汽气泡的成核，气泡脱离，以及随后液体对表面的再润湿。尽管取得了进展，但先前关于池沸腾（以及潜在的流沸腾）表面的工作并未涉及开发最佳表面形貌的合理方法。例如，成核沸腾传热（NBHT）随着润湿性的增加而降低，设计师必须考虑成核位置密度、相关气泡偏离直径以及与表面结构和流体相行为相关的频率。对于高表面润湿性，较小尺度的表面结构特征（如空腔）可以作为成核位点；对于低润湿性，空腔尺寸，而不是其拓扑结构，将占主导地位。因此，用粗糙度值来表征表面不足以解释沸腾曲线的变化：为了提高NBHT和临界热流密度，必须详细研究流体-表面耦合。EMBOSS汇集了来自布鲁内尔大学、爱丁堡大学和帝国理工大学的多学科研究人员，以及六个工业合作伙伴和一个合作者（Aavid Thermacore, TMD ltd, Oxford Nanosystems, intrinq Materials, Alfa Laval， CALGAVIN和Oxford lasers），他们在尖端微制造、实验技术以及分子、中介体和连续尺度建模和仿真方面具有专业知识。EMBOSS框架将为池沸热管理系统的操作原型的合理设计、制造和优化提供信息。设计的最佳性将根据材料和能源节约、热交换设备效率和足迹、减少排放和过程可持续性来衡量。与合作伙伴的合作将确保与工业需求保持一致，并将加速技术向工业的转移。这些合作伙伴将通过项目进展会议提供指导和建议，其中一些合作伙伴还将主持这些会议。此外，阿法拉伐将提供钎焊热交换器作为实验工作的冷凝器，Intrinsiq将提供涂层表面的铜墨水，Oxford nanoSystems将提供纳米结构的表面涂层。该项目将整合EPSRC繁荣成果和工业战略挑战基金在能源（弹性国家）、制造业和数字技术（弹性国家、生产性国家）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.