Collaborative Research: ISS: Probing Interfacial Instabilities in Flow Boiling and Condensation via Acoustic Signatures in Microgravity

流动沸腾和冷凝对于电子冷却，发电，制冷，水净化，化学处理等的高效和安全运行至关重要。两相流在液-气界面处也有很大的不稳定性。这些不稳定性会导致显著的热性能下降，降低传热系数，增加压降，并导致过热。为了防止工艺中断或热性能恶化，加强对不稳定机制的理解并对其进行持续监测至关重要。该项目旨在利用宽带声发射（AE）传感技术，通过声波测量和分析动态行为，探索微重力下主导流动不稳定性的物理机制。两相流是一种复杂的现象，许多物理机制同时对测量信号起作用，导致地面测试过程中的声学特征和固有噪声重叠。国际空间站（ISS）的长期微重力环境固有地解耦了两相流过程中物理机制的声学特征，并使研究主要传输机制成为可能。项目团队还将组织外展活动，制作海报、小册子、播客和视频等教育材料，解释国际空间站微重力环境带来的研究优势。本项目旨在利用宽带声发射传感技术对流动沸腾和冷凝过程中控制液-气界面不稳定性的输运机制进行基本理解，重点研究流动沸腾过程中的临界热流密度（CHF）、最大可达热流密度以及流动冷凝过程中的流态转换。该项目将通过三个具体目标填补这一广泛的知识空白。首先，在部署到国际空间站之前，将开发一个独立的声发射传感模块，并在实验室规模的测试中对单个传输过程进行基准测试，包括气泡偏离、湍流和毛细管流动。其次，将通过地面和微重力流动凝结试验探讨界面波和湍流扩散在流动凝结中的作用。后者将使用国际空间站上的流动沸腾和冷凝实验（FBCE）设备进行，并部署声学传感模块。第三，研究了流动-沸腾-流型转换和CHF过程中的主导输运机制。该项目将为流动沸腾和冷凝的界面不稳定性提供有价值的见解，这对于设计和优化冷凝器和锅炉以最大化传热和最小化能耗至关重要。该项目将对发电、半导体制造、化学加工和交通运输脱碳产生影响。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。

Flow boiling and condensation are crucial to the efficient and safe operation of electronics cooling, power generation, refrigeration, water purification, chemical processing, and among others. Two-phase flows are also subject to a wide range of instabilities at the liquid-vapor interface. These instabilities can lead to significant thermal performance degradation, reducing heat transfer coefficient, increasing pressure drop, and causing overheating. To prevent process disruptions or thermal performance deterioration, it is of utmost importance to enhance the understanding of instability mechanisms and continually monitor them. This project seeks to probe the physical mechanisms that dominate flow instabilities in microgravity using wideband acoustic emission (AE) sensing that measures and analyzes dynamic behaviors through acoustic waves. Two-phase flows are complex phenomena where many physical mechanisms simultaneously contribute to the measured signals, resulting in overlapping acoustic signatures and intrinsic noises during ground tests. The long-term microgravity environment on the International Space Station (ISS) inherently decouples the acoustic signatures of the physical mechanisms during two-phase flows and enables the examination of the leading transport mechanisms. The project team will also organize outreach events and create educational materials such as posters, brochures, podcasts, and videos to explain the advantages of research brought by the microgravity environment on ISS. This project aims to advance the fundamental understanding of the transport mechanisms that govern liquid-vapor interfacial instabilities in flow boiling and condensation using wideband AE sensing, with a focus on both the critical heat flux (CHF), the maximum achievable heat flux during flow boiling, and the flow regime transition during flow condensation. The project will fill this broad knowledge gap with three specific aims. First, a self-contained AE sensing module will be developed and benchmarked for individual transport processes including bubble departure, turbulence, and capillary flows in lab-scale tests before its deployment on ISS. Second, the role of interfacial waves and turbulent diffusion in flow condensation will be probed using both ground-based and microgravity flow condensation tests. The latter will be performed using the flow boiling and condensation experiment (FBCE) facility on ISS with the deployed acoustic sensing module. Third, the dominant transport mechanism during flow boiling flow regime transition and CHF will be examined. This project will provide valuable insights into interfacial instabilities of flow boiling and condensation, which are critical to the design and optimization of condensers and boilers that maximize heat transfer and minimize energy consumption. This project will make an impact on power generation, semiconductor manufacturing, chemical processing, and decarbonization of transportation.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.