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采用，可以在沸腾表面上产生极精细的粗糙度，从而极大地提高了它们的性能。然而，所有表面都容易受到污染，从而导致表面发生物理和化学变化，这可能会导致其性能发生巨大的、不可预测的变化，从而导致过热和故障的安全范围变得未知。本研究开发了一个用于了解沸腾过程的新框架，即使在表面退化的情况下也可以实时评估安全裕度，这可能会促进采用更先进的传热增强技术。同时，作为该项目的一部分，我们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，以展示诸如“蝴蝶效应”之类的混乱现象，这与该现象有一定的相似之处。随着混乱的沸腾过程。 PI 还将开发外展活动模块，让中学生到校园参加面向 STEM 的研讨会。拟议的研究将开发临界热通量 (CHF) 现象的模型，其中覆盖表面的蒸汽膜会导致热失控。该模型将寻求重现观察到的非线性现象，例如测量量的间歇性，将开发一个能够实现沸腾曲线无量纲化的理论框架，从而对导致 CHF 的条件（具体而言，成核位点）有更普遍的理解。互动将被纳入气泡增长模型中，以重现实验观察到的间歇性，这种间歇性预计会产生可以用赫斯特指数表示的长期时间相关性，并且将使用多重分形框架来分析实验数据。预计将显示预测的普遍行为，与系统参数无关。该研究将探讨赫斯特指数行为是否与表面粗糙度无关，从而使其能够用作充当签名的实时可观测量。为了了解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吸流动，这将产生有关之前条件的进一步信息。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。