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，广泛应用于发电厂，微电子和工业热交换器。近年来，用于制造电子产品的微加工技术已被用于在沸腾表面上产生极细尺度的粗糙度，从而极大地提高其传热性能。然而，所有表面都容易受到污染，这可能导致表面的物理和化学变化。这可能导致其性能发生戏剧性的、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。本研究开发了一个新的框架，了解沸腾过程，使评估的安全裕度在真实的时间，即使表面降解。除了提高安全性外，这还可以促进采用更先进的传热增强技术，同时提供对沸腾现象的更好的基本理解。 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，以说明与混沌沸腾过程有某些相似之处的“蝴蝶效应”等混沌现象。PI还将开发外展活动模块，将中学女生带到校园参加面向STEM的研讨会。 拟议的研究将开发一个模型的临界热通量（CHF）的现象，其中蒸汽膜覆盖的表面导致热失控。该模型将试图重现观测到的非线性现象，如测量量的不连续性。将开发一个理论框架，使无量纲的沸腾曲线，导致更普遍的理解导致CHF的条件。具体而言，成核位点的相互作用将被纳入气泡生长模型，以再现实验观察到的不稳定性的数量。这种不稳定性预计会产生长期的时间相关性，可以用赫斯特指数来表示。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，独立于系统参数。该研究将探讨赫斯特指数行为是否独立于表面粗糙度，使其能够用作实时可观察的量，作为即将发生故障的标志。为了了解观察到的趋势的原因，并协助模型开发，毛细作用下的离去气泡的流动将使用高速测温和全内反射显微镜的特点。这将产生进一步的信息，条件之前，立即开始的CHF和dryout.This奖项反映了NSF的法定使命，并已被认为是值得的支持，通过评估使用基金会的智力价值和更广泛的影响审查标准。

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.