Deciphering the Physics of Critical Heat Flux (CHF)

沸腾是一种常见的传热机制，从大多数建筑中使用的冷却和制冷系统到能源和过程工业中使用的大型锅炉，都有许多应用。沸腾换热过程的性能受到一种通常称为临界热流密度的现象的限制。临界热通量是加热器在形成将表面与液体隔离的低导热系数的蒸汽层之前可以与沸腾液体交换的最高热通量。尽管对临界热流密度的研究已有近一个世纪的历史，但由于相关现象是瞬变的、几何上的复杂的，并且受到多个耦合物理机制的限制，其背后的物理机制仍未被完全理解。该研究项目旨在解决有关临界热流密度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，如X波段雷达、激光二极管、基于半导体的电力变压器、数据中心和更可靠、更紧凑的核反应堆。这项研究的结果还将通过纳入沸腾换热物理的新知识来丰富热流体科学课程。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。这项建议的第一个目的是调查流体动力增强和可吸性之间的耦合。利用表面上方疏水膜的新结构来优化多相流，将确定流体动力、芯吸和液体压力对临界热流密度的贡献，并分别进行优化。该研究项目还旨在建立一个假设，即当使用特定几何形状的亚毫米翅片时，扩展面积比提高了临界热流密度。涉及低表面张力流体和高表面张力流体的大量实验、高速可视化和最先进的热流图将为验证、量化和概括上述贡献提供数据。这一努力的最终结果将是为临界热流密度的极限建立科学基础，并利用设计工具来最大化各种加热器材料和流体的临界热流密度。这项工作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开发，性能大大提高。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.