Collaborative Research: ISS: GOALI: Transients and Instabilities in Flow Boiling and Condensation Under Microgravity

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Extensive terrestrial studies have been conducted for over seventy years to develop, test and validate predictive theories for flow boiling and condensation as they occur in various applications in the petrochemical, pharmaceutical, biochemical, nuclear, and metallurgical industries. Once a boiling bubble forms on a heated surface, it soon grows large enough to detach from the nucleation site and travel with the flowing fluid. Evolution of boiling bubbles is governed by a delicate balance between the inertial, capillary, drag & lift hydrodynamic, and buoyancy forces. A small inaccuracy in measuring the bubble motion can lead to a large uncertainty in the interpretation of experimental data. Rigorous testing and validation of theories for two-phase flows at the individual bubble level remains a longstanding challenge. By eliminating strong buoyancy effects, long duration microgravity experimentation on the International Space Station's (ISS) Flow Boiling and Condensation Experiment (FBCE) Hardware offers a unique opportunity to study the role of capillary and hydrodynamic forces in the bubble growth and coalescence in a flowing fluid and condensate film. The project team will also participate in educational programs that use space themes to improve interest and skills in STEM by incorporating our project work into lesson plans and laboratory work for the benefit of college and high-school students. The proposed effort seeks to quantify the interactions between the flow field, temperature field, and phase distributions in flow boiling and condensation under transient and unstable conditions in the absence of gravity. Experiments will involve setting the ISS FBCE operating parameters and then recording the pressure and temperature responses within the system and imaging the two-phase flow. The focus is to force transients and instabilities in two-phase flows and to simulate system performance using numerical techniques. The ultimate goal is to see if theoretical predictions for boiling and condensation match up with the measurements in microgravity, and if not, to determine what is missing in the theories that is required to better match the experimental data. The project team will inspect the fine details of bubble dynamics using image analysis techniques, scrutinize the density-wave oscillations in two-phase flows, and correlate those with temperature and pressure-drop oscillations generated by the mechanical and thermal components in the system. Machine learning techniques will use microgravity experimental data to test and validate theoretical predictions models for phase-change fluid flows and enhance guidelines for the design of flow boiling and condensation equipment in terrestrial and gravity-independent applications.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.