Research and development of a semi-hermetic reciprocating compressor for transcritical CO₂ refrigeration cycle

A semi-hermetic reciprocating compressor was designed and developed for the transcritical carbon dioxide (CO₂) refrigeration cycle. In addition, a mathematical model was established to simulate the thermodynamic process in this transcritical CO₂ compressor. The internal leakage, heat transfer, and flows through the suction/discharge valves together with the valve motion were taken into account in the model. In order to evaluate the overall performance of the developed compressor, a test rig was built to measure the volumetric efficiency, isentropic efficiency, and coefficient of performance (COP), and also recorded the pressure-volume diagram. The calculated indicated power deviated by 4.16 per cent from the measured one, and the maximum deviations of the isentropic and volumetric efficiencies were-2.86 per cent and 4.87 per cent, respectively. Both the calculated and measured data showed that the compressor had a cooling COP of 2.0-3.2. As the pressure ratio increased from 2.3 to 3.5, the volumetric and isentropic efficiencies ranged from 0.70 to 0.86 and from 0.62 to 0.66, respectively. The recorded p-V diagram indicated that the power losses associated with the suction and discharge processes accounted for 4.6 per cent and 6.8 per cent of the total indicated power, respectively. The validated model can be used to investigate the thermodynamic process of the reciprocating CO₂ compressor with the aim of enhancing the compressor efficiency.