Helium Liquefaction System
Because Helium is very expensive on the open market, the 2nd Institute of Physics of the RWTH Aachen University runs a helium liquefaction system, that can recover used Helium.The liquefaction systems are situated in a separate building next to the Physikzentrum in order to keep the mechanical vibrations of the laboratories as low as possible.
In scientific research liquid helium is necessary as a cooling medium to reach very low temperatures. 4He condensates at a temperature of 4,2 K. By evaporation cooling it is even possible to reach temperatures down to 800 mK.
The commercially available helium liquefation system of the company “Linde” has an output-flow of up to 22 liters helium per hour.In combination with liquid nitrogen pre-cooling the production rate reaches 30 liter per hour. First the helium gas is purified from extrinsic gases. After that it is cooled down in three temperature steps by adiabatic expansion to at least 4,2 K. The liquid helium is stored in a 4200 liter reservoir. From the reservoir the helium is filled into 100 liter dewars which are carried to the helium consumers at the institutes of the RWTH. Beneath the physical institutes, also several chemical and semiconductor institutes are supplied with our liquid helium. The annual liquefaction rate is more than 85000 liters.
Helium recovery system
There are different reasons for helium losses in the circuit (precooling of the cryostats, gas-purification, diffusion while storing in gas-bundles, leakages, etc.). This part is replaced by purchasing helium from the open market. The leakage rate of the whole system is about 5 % helium gas per year.