The dimensioning of pressure relief devices (PRD) for helium cryostats requires detailed knowledge of the pressure increase during incidents. In case of the loss of insulating vacuum (LIV), this is induced by heat input due to deposition of atmospheric air on the surface of the helium vessel. Instead of considering the process dynamics, the dimensioning of PRD according to established standards is based on constant heat flux values, yielding potential oversizing. However, the heat flux depends on the rate of air reaching the cold surface, the thermal capacitance of and the heat transfer resistance inside the helium vessel, which are temperature-/time-dependent.
In order to improve the theoretical basis for the dimensioning of cryogenic PRD, this work presents a one-dimensional heat transfer model to calculate the heat flux dynamics based on dominating physical mechanisms. The results are compared with experimental data measured in the cryogenic safety test facility PICARD.