Results from neutron imaging phase change experiments with LH2 and LCH4

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Department of Mechanical Engineering-Engineering Mechanics


Predicting evaporation and cryo-storage behavior of liquid hydrogen poses a challenge for both terrestrial energy infrastructure and long term space missions. The current understanding of cryogenic phase change and subsequent boil-off is limited, in part, because the values of accommodation coefficients (inputs to phase change models) are still lacking and experimental data to compute them are severely limited. In order to determine the accommodation coefficients, a new cryo/neutron imaging experiment was developed. Tests were conducted in the BT-2 Neutron Imaging Facility at the National Institute of Standards and Technology (NIST) by introducing propellant vapor into cylindrical aluminum (Al 6061) and stainless steel (SS 316) cells placed inside a 70 mm cryostat. Saturation points between 80 kPa - 230 kPa were tested for liquid H2 and CH4. Phase change was induced through precise control of pressure and/or temperature. Neutron imaging was used to visualize the liquid and evaporation/condensation rates were determined through image processing. Both hydrogen and methane are perfectly wetting fluids as evidenced by the formation of micro-scale thin film at the onset of condensation and varies in thickness with rate of phase change. The rates of phase change are a function of both the size of the container and the degree of offset from saturation. The unique experimental data, made available through a data repository, have the potential to serve as a bench mark for future studies or serve as a dataset for model validation.

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