Deciphering the Physics of Critical Heat Flux (CHF)

沸腾是一种常见的传热机制，其应用范围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。沸腾传热过程的性能受到通常称为临界热通量的现象的限制。 临界热通量是加热器在形成将表面与液体隔离的低导热率的蒸气层之前可以与沸腾流体交换的最高热通量。 尽管对临界热通量的研究已经进行了近世纪，但由于相关现象是瞬态的、几何上复杂的并且受到多个耦合物理机制的限制，因此其基础物理仍然没有被完全理解。 本研究项目旨在解决关于临界热通量性质的基本物理问题。这项研究的结果可能有利于许多热管理是限制因素的应用，例如X波段雷达，激光二极管，基于晶闸管的电力变压器，数据中心和更可靠的紧凑型核反应堆。本研究之成果亦将丰富热流体科学课程，并将沸腾热传物理之新知识纳入其中。本研究旨在描述沸腾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。该建议的第一个目的是研究流体动力学增强和芯吸性之间的耦合。使用表面上方的疏水膜的新配置来优化多相流，流体动力学、芯吸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在扩展面积比提高临界热通量的假设上，当使用具有亚毫米级翅片的特定几何形状时。涉及低和高表面张力流体的大量实验、高速可视化和最先进的热通量测绘将提供数据来验证、量化和概括上述贡献。这项工作将最终在一个科学基础的限制，临界热通量和设计工具，以最大限度地提高临界热通量的广泛的加热器材料和流体。这项工作产生的基础知识和理论作为沸腾科学的主要验证门槛，可以促进下一代两相系统的开发，并大幅提高性能。该奖项反映了NSF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.