Helium liquefaction using a two stage Gifford McMahon Cryocooler

This paper describes helium liquefaction using a commercial cryocooler with 1.5 W cooling power at 4.2 K, equipped with heat exchangers for pre-cooling the incoming gas. No external cooling of helium gas or Joule-Thomson stages have been utilized. In this typical liquefaction system, helium gas at room temperature is initially pre-cooled by the cooling power available at the first stage of the cryocooler. Thereafter, it is cooled by the special heat exchanger (with large surface area) mounted on the second stage of the cryocooler. The gas when passing over the cold surface areas, gets condensed into a liquid and this enters the collecting vessel which is also mounted on the second stage of the cryocooler. A pressure gauge is connected to the collection vessel through a long narrow stainless pipe to monitor the vapour pressure of the liquid. When the liquid touches the end of this stainless steel pipe, thermoacoustic oscillations are observed on the pressure gauge, which is used for monitoring helium liquefaction. This paper describes the experimental setup and studies of liquefaction of helium by the cryocooler.