<ul><li>The NASA Engineering and Safety Center (NESC) has developed an analytical model that predicts diffusion between two gases during piston purging of liquid hydrogen (LH2) tanks.</li><li>The model helps explain dramatic helium savings seen in a recent Kennedy Space Center (KSC) purge and is applicable to future helium purges of the Space Launch System Core Stage LH2 tanks.</li><li>The purge was diffusion limited and could be modeled, leading to the conclusion that the flow rate should be increased until the onset of turbulent mixing and the purge should not be stopped to allow additional diffusion to occur.</li><li>A binary gas sensor was used to provide rapid real-time monitoring of the purge gas ratio, making the piston purging successful.</li></ul>

Helium Conservation by Diffusion Limited Purging of Liquid Hydrogen Tanks

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