Safety studies on vacuum insulated liquid helium cryostats

Christina Weber ,Carolin Zoller ,Andre Henriques ,Steffen Grohmann

doi:10.1088/1757-899x/278/1/012169

Abstract

The loss of insulating vacuum is often considered as a reasonable foreseeable accident for the dimensioning of cryogenic safety relief devices (SRD). The cryogenic safety test facility PICARD was designed at KIT to investigate such events. In the course of first experiments, discharge instabilities of the spring loaded safety relief valve (SRV) occurred, the so-called chattering and pumping effects. 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 than the commonly assumed 4W/cm2. This results in an oversized discharge area for the reduced relief flow rate, which corresponds to the lower heat flux.This paper presents further experimental investigations on the venting of the insulating vacuum with atmospheric air under variation of the set pressure (pset) of the SRV. Based on dynamic process analysis, the results are discussed with focus on effective heat fluxes and operating characteristics of the spring-loaded SRV.

Highlights

The dimensioning of cryogenic safety relief devices (SRD) requires detailed knowledge on the process dynamics, especially on the pressure increase and the heat ux trend following reasonable foreseeable accidents such as venting of the insulating vacuum with atmospheric air
The loss of insulating vacuum is often considered as a reasonable foreseeable accident for the dimensioning of cryogenic safety relief devices (SRD)
The cryogenic safety test facility PICARD was designed at KIT to investigate such events

Summary

Introduction

The dimensioning of cryogenic SRD requires detailed knowledge on the process dynamics, especially on the pressure increase and the heat ux trend following reasonable foreseeable accidents such as venting of the insulating vacuum with atmospheric air. Pumping occurred during these rst experiments and impermissible over-pressures and reduced discharge ow rates were observed [6]. Based on these results, further experimental investigations have been conducted, where the insulating vacuum is vented with atmospheric air. Smaller dimensions of the SRV are used compared to previous measurements and the results are discussed with focus on the SRV behaviour, the pressure increase inside the cryogenic vessel and the dynamic trend of the heat ux.

Experimental set-up

General dimensioning of safety relief devices

Heat ux evaluation

Experimental results

10 Opening pressure

Conclusion and outlook