Determination of Cryogenic Pool Boiling and Subsurface Helium Pressurization Characteristics in Reduced Gravity

Cryogenic propellants stored in low gravity may experience loss from pool boiling and the injection of gas directly into the liquid during pressurization. However, data to understand these dynamics are limited and do not reflect the characteristics of tanks used in flight (e.g., surface roughness and shape). This experiment was designed to determine cryogenic pool boiling in low gravity for flight-like surfaces and subsurface pressurization. The data collected will inform vehicle tank thermodynamic simulations to estimate heat and mass transfer rates and expected boiloff losses.

Problem Statement 

Zero-gravity boiling data is needed to predict boiloff loss of cryogenic propellants. Tank pressurization directly into the liquid may occur in zero gravity, generating boiloff and affecting the pressurization efficiency. Insufficient data on cryogenic subsurface pressurization is available, and heat/mass transfer rates are unknown. This experiment is designed to yield data for combining with computational fluid dynamics (CFD) simulations to back out heat and mass transfer rates.

Technology Maturation 

If successful, this experiment will provide zero-gravity pool boiling data for flight-like surfaces as well as subsurface pressurization data. Models generated from this data could enable accurate tank thermal and pressurization system design by minimizing uncertainty in propellant boiloff losses.

This work is a continuation of previous flight testing under T0035, T0172, and T0189. 

Summary of Flight Test
2022-11-15 During the week of November 14, 2022, a team of five graduate students and one post-doctoral research associate led by Professor Jacob Chung from the University of Florida Cryogenic Research Laboratory completed a reduced gravity parabolic flight campaign on board Zero-G Corporation’s G-Force One Boeing 727 aircraft. The team successfully performed the reduced gravity experiment and collected heat transfer and pressurization data for the microgravity pool boiling and helium subsurface pressurization in a simulated propellant storage tank. The team’s experimental system proved viable in extreme temperature changes and maintained integrity in microgravity and high G-forces during the research parabolic flights with ZERO-G Corporation. The results obtained from the reduced gravity experiment will be used to design and improve the test apparatus for their next reduced gravity flight campaign scheduled for May 2023. During the next flight campaign, the team is going to test new heater surface materials and different injection nozzles.
In-space cryogenic propulsion will play a vital role in NASA’s return to the moon. For this reason, long-term storage of cryogens will be required for lunar missions. Several, if not all, of the NASA lunar architecture elements will require storage and pressurization of cryogenic propellants, specifically the space tug and propellant tanker stages. This project is targeted at addressing the need to understand the propellant vaporization rates due to boiling and tank pressurization characteristics in microgravity. As noted in the NASA SSTIP, storage and transfer of cryogens in space is critical for deep space human exploration, making it one of the six NRC high priorities within the “Launch and In-Space Propulsion” Core Technology Investment.

This comprehensive model tests for both pool boiling and pressurization in a single experiment. It gathers relevant, validated, and wide-ranging data to inform computational fluid dynamics models. This would benefit future NASA missions and the commercial space industry.

Future Customers
• Space tugs, propellant tankers, and other lunar architectural elements
• Ascent and descent stages of spaceflight

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