CO2, positive displacement, novel compressor, prototype, rocker arm mechanism
Research activities towards developing CO2 compressors have increased drastically during the last couple years. Since the transcritical CO2 cycle operates at much higher absolute pressures as compared to the conventional vapor compression cycles, it is necessary to develop new compressors or modify existing ones. In this paper, a novel positive-displacement oil-free CO2 compressor will be introduced. The compressor’s mechanical linkage system will be described. In addition, preliminary compressor test results will be presented, including volumetric efficiency, overall isentropic efficiency, discharge temperature and mass flow rate. The compressor was designed and manufactured to provide cooling capacities from 10 kW to 100 kW. The novel compressor design introduces a new low-friction drive mechanism. The displacement of the compressor can be mechanically varied while keeping a small constant head clearance. A test stand was constructed to map the compressor efficiency, mass flow rate, power consumption and discharge temperature. The test stand is based on a hot gas bypass design, where parts of the discharged refrigerant flow bypasses the condenser, whereas the other part of the flow changes phase as it flows through a condenser. The two streams are mixed to obtain the desired compressor super heat at the suction side of the compressor. The prototype compressor has been tested under different pressure ratios (5, 4, 3, 2, 1.6) and at different speeds (900 rpm, 1200 rpm, 1500 rpm, 1800 rpm).