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型制动技术已被调整为在沸腾表面上产生极高的粗糙度，从而极大地增强了其传热性能。但是，所有表面都容易受到污染，可能会在表面引起物理和化学变化。这可能会导致其性能的巨大，不可预测的转变，从而导致安全性的安全余地在长期运行期间未知。本研究开发了一个新的框架，用于理解沸腾过程，即使表面降解，也可以实时评估安全幅度。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，同时对沸腾现象有更好的基本了解。作为该项目的一部分，适用于中学生的展览将与明尼苏达州的贝尔博物馆共同开发，以说明混乱的现象，例如“蝴蝶效应”，该现象与混乱的沸腾过程具有某些相似之处。 PI还将开发用于外展活动的模块，这些活动将中学女孩带到校园参加以STEM为导向的研讨会。拟议的研究将开发一个临界热通量（CHF）现象的模型，其中覆盖表面的蒸气膜导致热失控。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。将开发一个理论框架，以使沸腾曲线的非差异性，从而更普遍地了解导致CHF的条件。具体而言，核位点的相互作用将被纳入气泡生长模型中，以便重现实验观察到的间歇性数量。预计这种间歇性将引起赫斯特指数可以代表的长期临时相关性。实验数据将使用多重型框架进行分析，并有望显示预测的通用行为，而与系统参数无关。该研究将探讨赫斯特指数行为是否独立于表面粗糙度，从而将其用作实时可观察的数量，以充当即将发生故障的签名。为了了解观察到的趋势并有助于模型开发的原因，使用高速温度计和总内反射显微镜表征了起始气泡下的扇形流。这些将产生有关CHF和干旱发作之前紧接条件的进一步信息。该奖项反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响审查标准，被认为值得通过评估来获得支持。