Liquefaction of Helium and Nitrogen with GM Cryocooler

Abstract

The performance and reliability of cryocooler are continually improving. Consequently, the cryocooler based systems are also coming into the market and more frequently used by technical persons, scientists in their laboratory experiments or for commercial and space applications. The fundamental advantage of cryocooler is the small size of its cold head due to this it take little space and can be mounted on top of a Dewar, thus it helps in minimizing overall size of the cryocooler based setup. With this type of setup, it possible to fulfil the requirement of liquid helium and liquid nitrogen in laboratories where the consumption of liquid helium and liquid nitrogen is not in higher quantities. Dewar is used to store liquid cryogen, for production and storage purposes. We have developed a small-scale helium liquefaction systems and a nitrogen liquefaction system separately that provide solutions for liquid helium usage in laboratories. The helium liquefaction systems use two-stage GM cryocooler with 1.5 W cooling power at 4.2 K (Sumitomo modelSRDK-415D with compressor CSW-71D, consuming 6.5 kW electrical power) to provide cooling and condensation at 4.2 K and the nitrogen liquefaction system use a Cryomech Single stage Gifford-Mcmahon cryocooler to provide cooling and condensation of nitrogen at 80 K with the refrigeration capacity of 266 W (Rated) at 80K. The cold head/liquefier resides inside of the neck of a dewar in both helium and nitrogen liquefaction system. The room temperature helium gas to be liquefied enters the neck of the dewar and is efficiently pre-cooled by cold head before being liquefied. The two-stage GM cryocooler with 1.5 W cooling power at 4.2 K (Sumitomo model SRDK-415D with compressor CSW-71D, consuming 6.5 kW electrical power), equipped with heat exchanger at 2nd stage for condensing the incoming precooled gas by exposing larger surface area. No additional cooling power of cryoliquids or additional Joule–Thomson stages was utilized in case of helium and nitrogen liquefaction system. Measurements of the pressure dependence of the liquefaction rate were performed in both case of liquefaction system. The assembly of two-stage Gifford -McMahon cryocooler with heat exchangers and helium liquefaction container is usually accomplished in helium liquefaction system and the assembly of single stage GM cryocooler with heat exchangers and nitrogen liquefaction container is usually accomplished in nitrogen liquefaction system. The pressure gauge has to be connected to the container in both type of liquefaction system to examine the oscillation that gives the liquefaction rate. Also diodes are placed on the container to measure the temperature of helium and nitrogen at different stages in container. A maximum value of 10.5 SLPM was obtained for 2.5-3 psi stabilized pressure of cryostat in case of helium liquefaction system. . In the event of nitrogen liquefaction system maximum liquefaction rate of 74.36 Ltr/day was obtained at 3psi stabilized pressure of cryostat in case of the experimental dewar. We have also varied the pressure from 3psi to 15 psi to increase the liquefaction rate in the event of nitrogen liquefaction system and production rate varies from 74.36 Ltr/day to 80 Ltr/day was obtained.