Conveners
R&D in Cryogenic Safety: (1/2)
- Laurent Jean Tavian (CERN)
R&D in Cryogenic Safety: (2/2)
- Philippe Lebrun (CERN)
The dimensioning of cryogenic safety relief devices requires detailed knowledge on the process dynamics following the quench of superconducting magnets or the break of the insulating vacuum. In established standards and design codes, the sizing of cryogenic safety relief devices is based on constant (maximum) heat flux data, which potentially leads to oversized safety relief devices. Beside...
The presented work focuses on the risk analysis and the consequences of the unexpected leak to the tunnel of cryogenics gases. Formation of the gas mixture and its propagation along tunnels is an important issue for the safe operation of cryogenic machines, including superconducting accelerators or free electron lasers. As the cryogenics gas the helium and argon will be considered. A minimal...
The test facility PICARD, which stands for Pressure Increase in Cryostats and Analysis of Relief Devices, has been designed, constructed and commissioned for cryogenic safety experiments. With a cryogenic liquid volume of 100 liter, a nominal design pressure of PN16 and helium relief flow rates up to 4 kg/s, the test facility allows the systematic investigation of hazardous incidents in...
To perform the sizing of a safety device, the first step is the estimation of the heat flux arriving on the surfaces of the component to protect. The only reliable way to know this parameter is to perform experiments. Different tests have been done in the past by different teams but never with components filled with helium and discharging in supercritical state. CEA/SBT has in operation a test...
The selection process for size in safety equipment for cold vessels or process pipes in cryogenic systems should take into consideration the incidental ventilation of the vacuum vessel with atmospheric air. In this case, a significant heat input toward the cold elements of the system can be expected. A number of experimental investigations have been done for the elements at liquid helium...
It is proposed to discuss a general method for sizing the safety devices, for cryogenic fluids and whatever the thermodynamic states. In particular the interesting case of the two-phase subcritical discharge will be addressed.
The calculation is separated in three operations:
o The estimation of the loads arriving on the component to protect,
o The calculation of the mass flow to...
Liquid helium is widely used as a cooling agent for superconducting magnets. In case of an incident such as a magnet quench, the pressure in liquid helium cryostats increases rapidly. Hence, the cryostat has to be protected against overpressure by relieving the helium through a safety device, e.g. a safety valve. The discharge mass flow rate is limited by the so-called chocked flow in the...
In Industry sizing of safety valves for two-phase flow is still a challenge. Hazard analysis to identify the worst case scenaio, mechanical and thermodynamic non-equilibrium conditions to estimate the mass flow rate and multiple critical flow conditions are among others topics that may lead to differences in sizing a safety valve of up to 1 order of magnitude. There are more than 20 models...
Saturation of steam/water mixture flow and flashing initial sub-cooled flow inside throttling devices (i.e., safety and control valves) is investigated here. Due to thermal non-equilibrium and mechanical non-equilibrium effects, this phenomenon is of actual interest in the research community. Thermal non-equilibrium effect is accounted for boiling delay before vaporization when flow...
The flow of cold helium in pipes is a fundamental issue of any cryogenic installation. Pipelines for helium transportation can reach lengths of hundreds of meters. The proper selection of size for individual pipelines and safety valves is a crucial part in the consideration of costs for the entire installation and its safe operation. The size of the safety valve must be properly designed in...
