ISS: Transient Behavior of Flow Condensation and Its Impacts on Condensation Rate

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Condensers, which are used to reject heat and return/collect liquid to the evaporators/boilers, are essential parts of any liquid-vapor two-phase systems such as heat pipes and vapor chambers, water recovery and harvest, vapor compression systems, and Rankine cycle power systems. However, due to the dominant filmwise condensation mode, where vapors are condensed in the form of a film that covers the surface, in industry practice, condensation heat transfer rate is typically several folds lower than that of boiling or evaporation, leading to oversized- and overweighted-condensers. Highly efficient flow condensation is greatly desirable. Two-phase flow instabilities or oscillations in flow boiling and condensation can have detrimental effects on the system. Although extensive efforts have been taken to understand and manage the two-phase oscillation in flow boiling, only a few studies have been conducted in understanding two-phase condensing flow instabilities. This project would provide valuable knowledge and lead to novel control strategies in achieving the desirable flow pattern. If successful, this research project would improve not only the stability of condenser operations, but also the efficiency if two-phase oscillations can be properly utilized to enhance flow condensation. This project also offers a unique opportunity to promote interdisciplinary collaborations among thermal science, space technology, and machine learning. These types of collaborations would greatly benefit the communities of thermal science, machine learning, space industry, terrestrial water-energy industries, stakeholders, and science and technology education.The research objectives are to understand transient behaviors of flow condensation and their impacts on flow condensation rate in both ground and microgravity environments. New knowledge obtained in this study would advance understandings of operation parameters that govern flow condensation oscillations. The research objectives can be realized in five tasks: (a) systematically characterizing transient behaviors of flow condensation, (b) understanding the dependence of different two-phase flow patterns on the vapor flow changing rate and/or cooling rate, (c) identifying the range of operation conditions that generate intensive two-phase oscillations; (d) characterizing the influence of oscillation modes on flow condensation rate with an emphasis on enhancing flow condensation; and (e) developing machine-learning-based models to accurately predict transient behaviors of flow condensation, flow condensation rate and pressure drop, which are more accessible than the traditional two-phase experiments to research communities, industries, students, and the general public.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.