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This STTR-II-E effort concerns technologies related to cryogenic propellant production, storage, transfer, and usage to support NASA’s in-situ resource utilization (ISRU) goals. They include a broad range of applications, scales, and environments consistent with future NASA missions to Mars and beyond.
More specifically, the project addresses a well-known gap of cryogenic pool boiling measurements in reduced gravity environments for relevant surfaces and materials, which would ultimately be used to develop a correlation for boiling heat flux versus wall superheat in reduced gravity. The new reduced gravity data will also be available to NASA engineers to anchor their future models.
The primary reason for launching the STTR study is that cryogens constitute a unique family of low-boiling-point fluids whose thermophysical property trends are distinctly different from those of common fluids such as water, dielectric coolants, and refrigerants, for which the vast majority of data is available in the open literature.
The STTR-II study has been successful at acquiring and amassing cryogenic pool boiling data available in the literature and showed that there is a clear lack of data available in reduced gravity conditions. Additionally, the available data is not relevant for solid surfaces representative of cryogenic tank materials. The data obtained from this study will aid in understanding the effects of reduced gravity on cryogenic pool boiling that will facilitate the creation of a reduced-gravity cryogenic-data anchored correlation for heat flux versus wall superheat, and for possible anchoring of future tools to reduced gravity data.
Problem Statement
This project aims to address one of NASA Space Technology Mission Directorate’s top priority shortfalls concerning cryogenic propellant storage and transfer in reduced gravity environments. The project is directly related to Topic 1 of the original solicitation: “Supporting Sustainable Lunar Exploration and the Expansion of Economic Activity into Cislunar Space,” second bullet: “Long-term storage and transfer of fuels and processed materials, typically in a cryogenic state, on the lunar surface and in orbit.” This STTR-II-E work constitutes a major improvement from the STTR-II study: Providing the first methodology to predict the effects of reduced gravity (microgravity, Lunar, Martian) on pool boiling heat transfer, which is of paramount importance across multiple NASA systems and applications.
Goals & Objectives
1. Develop a test matrix for the parabolic flight experiments to ensure adequate coverage of the effects of reduced gravity on pool boiling heat transfer.
2. Devise functional parameters that would enable modifying the correlations developed during the STTR-II project to account for reduced gravity effects.
3. Update the consolidated cryogenic pool boiling database developed during the STTR-II project with the new reduced gravity data.
4. Retrofit the cryogenic pool boiling correlations developed during the STTR-II project to account for the effects of reduced gravity captured during the flight experiments.
5. Summarize the series of user-friendly correlations for the different regions and transition points of the pool boiling curve.
6. Combine the correlations to develop a method for generating a complete, continuous pool boiling curve for different cryogenic fluids.
Technology Maturation The flight test will enable updating the consolidated cryogenic pool boiling database developed during the STTR-II project with the new reduced gravity data.
The final correlations would ultimately be used for design and analysis of future space systems as stand-alone correlations, or could be inserted into NASA’s lumped node codes, such as Thermal Desktop or the Generalized Fluid System Simulation Program (GFSSP).
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