Deciphering the Physics of Critical Heat Flux (CHF)

沸腾是一种常见的传热机制，有许多应用，从大多数建筑物中使用的冷却和制冷系统到能源和加工工业中使用的大型锅炉。沸水传热过程的性能受到一种通常称为临界热通量的现象的限制。临界热流密度是加热器在形成将表面与液体隔离开来的低导热蒸汽层之前与沸腾流体交换的最高热流密度。尽管对临界热通量的研究已经进行了近一个世纪，但由于相关现象是短暂的，几何上复杂的，并且受到多种耦合物理机制的限制，其潜在的物理性质仍然没有完全理解。本研究项目旨在解决临界热通量性质的基本物理问题。这项研究的结果可能会使许多热管理是限制因素的应用受益，例如x波段雷达，激光二极管，半导体电力变压器，数据中心和更可靠的紧凑型核反应堆。本研究的结果也将丰富热流体科学课程，包括沸腾传热物理的新知识。本研究项目旨在描述沸腾过程中临界热流密度的物理机制，并为各种流体提供最大化临界热流密度的设计规则。本提案的第一个目的是研究水动力增强和弹性之间的耦合。利用表面上疏水膜的新配置来优化多相流，流体力学、排芯和液体压力对临界热通量的各自贡献将被识别并单独优化。该研究项目还旨在建立一个假设，即当使用亚毫米鳍的特定几何形状时，扩大面积比可以提高临界热流密度。一系列涉及低和高表面张力流体、高速可视化和最先进的热流图的广泛实验将提供数据来验证、量化和概括上述贡献。这一努力最终将为临界热流密度的极限建立科学基础，并为各种加热器材料和流体提供最大化临界热流密度的设计工具。在这项工作中产生的基本知识和理论是沸腾科学的主要验证门槛，可以促进下一代两相系统的发展，从而大大提高性能。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Boiling is a common mechanism of heat transfer that has numerous applications ranging from cooling and refrigeration systems used in most buildings to large boilers used in energy and process industries. The performance of the boiling heat transfer process is limited by a phenomenon commonly known as the critical heat flux. Critical heat flux is the highest heat flux a heater can exchange with a boiling fluid before the formation of a vapor layer of low thermal conductivity that isolates the surface from the liquid. Despite nearly a century of research on critical heat flux, its underlying physics is still not fully understood because the relevant phenomena are transient, geometrically complex and limited by multiple, coupled physical mechanisms. This research project aims to address fundamental physical questions about the nature of critical heat flux. Outcomes of this research could potentially benefit many applications in which thermal management is a limiting factor, such as X-band radars, laser diodes, semiconductor-based power transformers, data centers and more reliable, compact nuclear reactors. The results of this study also will enrich thermofluid science courses through inclusion of new knowledge on physics of boiling heat transfer. This research project aims to describe the physical mechanisms of critical heat flux in boiling and to provide design rules to maximize critical heat flux for a wide range of fluids. The first aim of this proposal is an investigation of the coupling between hydrodynamic enhancement and wickability. Using the new configuration of a phobic membrane above the surface to optimize multiphase flows, the respective contributions of hydrodynamics, wicking and liquid pressure on critical heat flux will be identified and individually optimized. This research project also aims to build on the hypothesis that extended area ratios enhance critical heat flux when specific geometries with sub-millimeter fins are used. An extensive array of experiments involving low and high-surface tension fluids, high-speed visualization and state-of-the-art heat flux mapping will provide the data to validate, quantify and generalize the above contributions. The effort will culminate in a science base for the limits of critical heat flux and with design tools to maximize critical heat flux for a wide range of heater materials and fluids. The fundamental knowledge and theories generated under this work serve as major validation thresholds in boiling science that can facilitate development of next generation two-phase systems with a drastically improved performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.