Water-lubricated, screw compressor, indicator diagrams, efficiency, mechanism
In recent years, water-lubricated screw compressors have attracted more and more attention, because this type of compressors can produce the high quality air completely free of oil and there is no contamination. However, poor sealing and lubricating properties of water might result in different operating characteristics compared with those of oil-injected compressors. A good understanding of the operating mechanisms is essential in any attempt to increase the performance of the compressor, which can be achieved by means of the indicator diagram. In this paper, a prototype of the water-lubricated screw air compressor was developed and a test rig was established. A series of pressure transducers were arranged in consecutive positions of the casing to measure the pressure distribution inside working chamber of the compressor. In addition, volumetric efficiency, adiabatic efficiency and mechanical efficiency of the compressor under different operating conditions were calculated based on measured volumeric flow-rate and power consumption. As a result, the influence mechanisms of rotating speed, discharge pressure and water injection flow-rate on the compressor performance and working process were analyzed based on indicator diagrams.