Design and Performance of Helium Liquefier based on GM Cryocooler

Abstract

Cryocooler based liquefiers are very popular in the production of liquid cryogenes in small amounts to meet the requirement of laboratory experiments, cryostats like MRI, PPMS, MPMS and MEG etc. They will take very less power input and produce liquid within few hours. These are very cheap and easy to maintain when compared to the liquefaction plants.
A small helium liquefier has been designed and developed in IUAC for the requirement of continuous supply of Liquid helium for OXFORD 8T PPMS (Physical Property Measurement System) cryostat. The cryostat requires liquid helium at the rate of 15 - 18 liters per day (12 liters per day in static condition). We used Sumitomo make SRKD-415 D two stage GM cryocooler which has 2nd stage refrigeration capacity of 1.5 W at 4.2 K. The liquefier operates on the principle of thermo-siphon loop in which the fluid circulates without the requirement of external pump. In start up phase, the helium gas is supplied from high pressure gas cylinder until the liquid helium reaches the required level in cryostat. Once it reaches, the supply from cylinder is stopped and the evaporated helium gas from the cryostat is captured and feeds to the liquefier inlet through the external path provided. It continuously liquefies the evaporated helium gas without the requirement of extra helium gas from cylinder. Two heat exchangers are provided for 1st stage and 2nd stage for efficient heat transfer between the cryocooler and helium gas. The gas is precooled at 1st stage regenerator and 2nd stage regenerator through natural convection phenomenon. An experimental helium dewar is fabricated to test the performance of helium liquefier. It produces the liquid helium at the rate of 12 liters per day continuously and re-liquefies the same helium gas for longer durations.
We have conducted experiment to know the thermal behaviour of intermediate stage between 1st stage and 2nd stage of cryocooler on the extraction of available extra cooling effect. We have introduced 3 baffles along the regenerator wall and give heat input from 0 W to 10 W while the both stages are at specified capacity. We also studied the design parameters of fin type condenser where it mostly depends on the properties of liquid.