30 September 2004 Helium cryostat vent sizing For SOFIA science instruments
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Abstract
In the event of a cryostat vacuum failure, the subsequent liquid helium boil off can produce a significant pressure rise in the helium reservoir potentially causing damage to the cryostat. To preclude cryostat damage during such a failure, an analysis has been developed to predict the maximum internal pressure for the corresponding vent neck size and helium reservoir surface area at failure condition. To demonstrate that the analysis predicts correct pressure values, a series of experiments have been carried out at NASA Ames Research Center to measure the pressure profile during an induced failure. The maximum measured helium reservoir pressure is then used in the analysis to derive the heat load. The experiments have been conducted using a cylindrical helium and nitrogen cryostat with a variable size constriction insert in the helium neck to enable measuring the pressure rise across a range of effective neck areas. The experimentally derived heat flux on the uninsulated helium reservoir during an induced vacuum failure is 3.1 ± 0.2 W/cm2. Some preliminary test results are presented describing the effects of superinsulation, but this aspect of cryostat design is not extensively explored, as the design and materials selected may have highly variable results.
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Maureen L. Savage, Siriluk Limmongkol, Richard E. Bacher, Theodore M. Brown, Christopher T. Koerber, Eric Smith, Patrick G. Waddell, "Helium cryostat vent sizing For SOFIA science instruments", Proc. SPIE 5492, Ground-based Instrumentation for Astronomy, (30 September 2004); doi: 10.1117/12.552622; https://doi.org/10.1117/12.552622
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