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

职业：池沸腾中热波动的普遍动力学及其在预测临界热通量中的作用

• 批准号: 2145075
• 负责人: Vinod Srinivasan
• 金额: $ 57.8万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-06-01 至 2027-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2145075&HistoricalAwards=false
• 关键词: CAREER; Universal; Dynamics; Thermal; Fluctuations

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.

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加工技术已经适应于在沸腾表面上产生极其精细的粗糙度，极大地提高了它们的传热性能。然而，所有的表面都容易受到污染，从而导致表面的物理和化学变化。这可能导致它们的性能发生巨大的、不可预测的变化，其结果是，在长期运行中，过热和故障的安全边际变得未知。目前的研究开发了一个新的框架来理解沸腾过程，即使在表面降解的情况下，也可以实时评估安全边际。除了提高安全性外，这可能会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。作为项目的一部分，一个适合中学生的展览将与明尼苏达州的贝尔博物馆联合开发，以说明混乱现象，如“蝴蝶效应”，这与混乱的沸腾过程有一定的相似之处。PI还将开发外联活动模块，将中学女生带到校园参加以stem为导向的讲习班。提出的研究将建立一个临界热通量（CHF）现象的模型，其中覆盖表面的蒸汽膜导致热失控。该模型将试图再现观测到的非线性现象，如测量量的间断性。将开发一个理论框架，使沸腾曲线的无量纲化，导致对导致CHF的条件的更普遍的理解。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性。这种间断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。该研究将探索赫斯特指数的行为是否与表面粗糙度无关，从而使其成为一个实时可观察的量，作为即将发生故障的标志。为了理解所观察到的趋势的原因并协助模型开发，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流。这将提供关于发生CHF和干枯之前情况的进一步信息。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。