CAREER: Universal Dynamics of Thermal Fluctuations in Pool Boiling and Their Role in Predicting Critical Heat Flux

沸腾是一种高效的传热机制，广泛应用于电厂、微电子、工业换热器等领域。近年来，用于制造电子产品的微细加工技术已经被采用，在沸腾表面上制造出超细尺度的粗糙度，极大地提高了它们的传热性能。然而，所有表面都容易受到污染，这可能会导致表面发生物理和化学变化。这可能会导致它们的性能发生戏剧性的、不可预测的变化，结果是在长期运行期间，过热和故障的安全裕度变得未知。本研究为理解沸腾过程开发了一个新的框架，即使在表面退化的情况下，也能够实时评估安全裕度。除了提高安全性，这还可以促进采用更先进的传热强化技术，同时更好地从根本上了解沸腾现象。作为该项目的一部分，将与明尼苏达州贝尔博物馆联合开发一个适合中学生的展览，以展示混沌现象，如与混沌沸腾过程有一定相似之处的蝴蝶效应。国际和平协会还将开发外展活动模块，将中学女生带到校园参加以STEM为导向的讲习班。这项拟议的研究将开发一个临界热通量(CHF)现象的模型，在该现象中，覆盖表面的蒸汽膜会导致热失控。该模型将试图重现观测到的非线性现象，如测量量的间歇性。将开发一个理论框架，使沸腾曲线无量纲化，从而更普遍地理解导致充血性心力衰竭的条件。具体地说，成核位置的相互作用将被纳入气泡生长模型，以便在数量上再现实验观察到的间歇现象。这种间歇性预计将产生可由赫斯特指数表示的长期时间相关性。实验数据将使用多重分形框架进行分析，并有望显示预测的普遍行为，而不依赖于系统参数。这项研究将探索赫斯特指数行为是否独立于表面粗糙度，从而允许将其用作实时可观测的量，作为即将到来的故障的标志。为了了解观察到的趋势的原因，并帮助模型的建立，将使用高速测温和全内反射显微镜来表征离开气泡下的芯吸流动。这项裁决反映了NSF的法定使命，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 highly efficient heat transfer mechanism widely used in power plants, micro-electronics, and industrial heat exchangers. In recent years, microfabrication technology used for manufacturing electronics has been adapted to create extremely fine-scale roughness on boiling surfaces, tremendously enhancing their heat transfer performance. However, all surfaces are prone to contamination that can cause physical and chemical changes on the surface. This can lead to dramatic, unpredictable shifts in their performance, with the result that the margin of safety from overheating and failure becomes unknown during long-term operation. The present study develops a new framework for understanding the boiling process that enables assessment of the safety margin in real time, even as the surface degrades. Besides improving safety, this may promote adoption of more advanced heat transfer enhancement techniques, while providing a better fundamental understanding of the boiling phenomenon. As part of the project, an exhibit appropriate for middle schoolers will be developed jointly with the Bell Museum of Minnesota, to illustrate chaotic phenomena such as the ‘butterfly effect’, which has certain parallels with the chaotic boiling process. The PI will also develop modules for outreach activities that bring middle school girls to campus for STEM-oriented workshops. The proposed research will develop a model for the Critical Heat Flux (CHF) phenomenon, in which a vapor film blanketing the surface leads to thermal runaway. The model will seek to reproduce observed nonlinear phenomena such as intermittency of measured quantities. A theoretical framework will be developed that enables non-dimensionalization of the boiling curve, leading to a more universal understanding of the conditions leading to CHF. Specifically, nucleation site interactions will be incorporated into bubble growth models in order to reproduce the experimentally observed intermittency in quantities. This intermittency is expected to give rise to long-term temporal correlations that can be represented by the Hurst exponent. Experimental data will be analyzed using a multifractal framework, and are expected to display the predicted universal behavior, independent of system parameters. The study will explore whether the Hurst exponent behavior is independent of surface roughness, allowing it to be used as a real-time observable quantity that acts as a signature of impending failure. In order to understand the reasons for the observed trends and assist in model development, the wicking flow under a departing bubble will be characterized using high-speed thermometry and total internal reflection microscopy. These will yield further information on conditions immediately preceding the onset of CHF and dryout.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.