Numerical and experimental study on characterization of oil-free linear compressor

The precooled Joule-Thomson (JT) cryocoolers driven by linear compressors working at liquid helium temperature have the advantages of simple and compact structure, low vibration and electromagnetic interference. To explore the feasibility of single-stage oil-free linear compressor with high pressure ratio driving JT cryocooler working at liquid helium temperature, performance testing and optimization research on a linear compressor are conducted. The operating mechanism of a linear compressor is introduced and the compressor experiment setup is built. When the low pressure is maintained at about 0.101 MPa with helium as the working fluid, the compressor achieves a groundbreaking pressure ratio of 10 and the corresponding mass flow rate is 7.5 mg/s. The stable working condition of compressor is quantified at pressure ratio of 5-10 and mass flow rate of 2.6-14.0 mg/ s, enabling thermodynamic optimization that reveals a peak exergetic efficiency of 39.4 % at a pressure ratio of 5 and a mass flow rate of 13.5 mg/s. An original numerical model developed using Sage software and calibrated with experimental data, demonstrates exceptional accuracy, with average relative deviations of 2.65 % (pressure) and 4.33 % (mass flow rate) between simulations and experiments. The results verified the rationality of the linear compressor model. Based on the results, potential optimal design for linear compressors were provided.