Investigation of neon–nitrogen mixed refrigerant Joule–Thomson cryocooler operating below 70 K with precooling at 100 K

• Ne–N2 mixed refrigerant Joule–Thomson refrigerator is designed and tested for cooling temperature from 64 K to 70 K.
• The achieved minimum temperature was 63.6 K when the pressure after the expansion valve was maintained by 130 kPa.
• Carnot efficiency of present cryocooler shows 6.5%.
• Refrigeration cycle with Ne–N2 binary mixture can be accurately designed and predicted with Peng–Robinson equation of state.

There has been two-stage mixed refrigerant (MR) Joule–Thomson (JT) refrigeration cycle suggested for cooling high temperature superconductor (HTS) electric power cable below 70 K. As the continuation effort of realizing the actual system, we fabricated and tested a small scale neon and nitrogen MR JT cryocooler to investigate the refrigeration characteristics and performance. The compression system of the refrigeration circuit was accomplished by modifying commercially available air-conditioning rotary compressors. Compressors stably operated at the maximum compression ratio of 31 when the suction pressure was 77 kPa. The achieved lowest temperature was 63.6 K when the heating load was 35.9 W. The measured Carnot efficiency of the present system was 6.5% which was lower than that of the designed goal of 17.4%. The low efficiency of compressor (34.5%), and the pressure drop at the compressor suction were the main reasons for this efficiency degradation. The feasibility and usefulness of neon and nitrogen MR JT refrigeration cycle was validated that the achieved minimum temperature was 63.6 K even though the pressure after the expansion was maintained by 130 kPa. The comparison between the measurement and calculation showed that each stream temperature of refrigeration cycle were predictable within 3% error by Peng–Robinson equation of state (EOS).