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

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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.