Speaker
Description
The loss of insulating vacuum is often considered as a reasonable foreseeable accident for the dimensioning of cryogenic safety relief devices. The cryogenic safety test facility PICARD was designed to investigate such events. In the course of first experiments, discharge instabilities of the spring loaded safety relief valve occurred, the so-called chattering and pumping. These instabilities reduce the relief flow capacity, which leads to impermissible over-pressures in the system. The analysis of the process dynamics showed first indications for a smaller heat flux at opening pressure than the commonly assumed 4 W/cm2, resulting in an oversized discharge area for the correspondingly reduced relief flow rate.
This contribution presents further experimental investigation, where the insulating vacuum was vented with atmospheric air under variation of the venting diameter, the size and the set pressure of the safety relief valve and the helium filling level. Based on dynamic process analysis, the results are discussed in terms of effective heat fluxes and operating characteristics of the spring-loaded safety relief valves.