Development of a high efficiency joule-thomson refrigerator below 77 K

Abstract

Joule-Thomson (JT) refrigerator is widely used for domestic fridge, air-conditioning systems for cars and buildings for its simple structure, low cost, high reliability, and high efficiency. JT refrigerator is also successfully applied in cryogenic refrigeration by adopting several modifications such as using heat exchanger, addition of precooling stage, using mixed refrigerant (MR), and a super insulation. Usual MR JT refrigerators exhibit good performance at refrigeration temperature above 80 K. A precooled neon and nitrogen MR JT refrigerator was designed for cooling temperature below 77 K. The coefficient of performance (COP) of the proposed MR JT refrigerator was predicted as 0.058 at 70 K (19.2% for Carnot efficiency) with the optimization of design parameters. COP could be improved further to 0.064 by enhancing the efficiency of precooling cycle. As the continuation effort of realizing the actual system, a small scale neon and nitrogen MR JT refrigerator was constructed to investigate the refrigeration characteristics and the performance. The compression system of the refrigeration circuit was accomplished by the modification of 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 of MR JT refrigerator was 63.6 K when the cooling capacity was 35.9 W. The measured Carnot efficiency of the present system was 6.5% which was lower than that of the designed value of 17.4%. The low efficiency of compression system (34.5%), and the pressure drop in the compressor suction were the main reasons for this efficiency deterioration. The feasibility and usefulness of neon and nitrogen mixture for the MR JT refrigerator was validated because the achieved lowest temperature was 63.6 K even though the pressure after the JT expansion was maintained by 130 kPa. The comparison between the measurement and the calculation shows that ...