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Cryogenic Liquid Heat Transfer Analysis

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Rept. for 24 Jun-30 Aug 87

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The objective of the present study was to determine if there is a suitable cryogenic fluid which could serve to simulate the liquid hydrogen LH2-induced loads and stresses during structural strength testing of large space transportation systems. Liquid helium LHe and liquid nitrogen LN2 were identified early on as the only pure cryogenic fluids which needed to be considered. Neon, while being a promising candidate based on its cryogenic properties, simply is not available in large enough quantities to warrant consideration. The study showed that the primary factor to be considered in choosing a simulant was the magnitude of the heat leakage rate that could be expected to apply to the structure. Analysis of several generic hydrogen fuel tank designs showed that heat leaks in the range of 100 to 500 Btuhr-sq ft could be expected. Expressed in alternate terms, this would roughly correspond to LH2 boil-off rates of 10 to 30 percent per day. Based primarily on heat transfer considerations it was concluded that LHe essentially duplicates LH2 thermal effects providing the tank pressure of the test vehicle is less that 26.6 psia 0.183 mPa. It was also found that liquid nitrogen duplicates LH2 effects providing the 57 deg K difference in boiling temperatures of these two cryogens is accounted for. It was also determined that real difficulties can be expected in simulating LH2 effects in the ullage space of a fuel tank. Based on heat transfer considerations, it is shown that helium as a simulant will over-cool the tank walls around the ullage space and the opposite is true for nitrogen.

Subject Categories:

  • Inorganic Chemistry
  • Thermodynamics
  • Liquid Rocket Propellants

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