Performance Enhancement in Sliding Vane Rotary Compressors through a Sprayed Oil Injection Technology

摘要

In Sliding Vane Rotary Compressors, as well as in most of positive displacement machines, the oil is injected tornaccomplish sealing and lubrication purposes. However, the oil injection could produce an additional outcome duringrnthe compression phase with a great saving potential from the energetic point of view. Being the air inside the cellrnat a higher temperature than the oil injected, a cooling effect could be achieved so decreasing the mechanical powerrnrequired for the compression. At the moment, the oil is introduced inside the compressor vanes simply through a seriesrnof calibrated holes that are only able to produce solid jets. In this way any effective heat transfer is prevented, asrndemonstrated by p-V measurements inside the cells during the compression phase.rnIn the current study, a theoretical model of a sprayed oil injection technology was developed and further experimentallyrnvalidated. The oil was injected along the axial length of the compressor through a number of pressure swirl atomizersrnwhich produced a very fine spray. The conservation equations, solved with a Lagrangian approach, allowed to trackrnthe droplets evolution from the injection until the impingement onto the metallic surfaces of the vanes. The theoreticalrnapproach assessed the cooling effect due to the high surface to volume ratio of the droplets and a reduction of thernindicated power was predicted. The model validation was carried out through a test campaign on an mid-size slidingrnvane compressor equipped with a series of pressure swirl injectors. The reconstruction of the indicator diagram asrnwell as the direct measurements of torque and revolution speed revealed a reduction of the mechanical power absorbedrnclose to 7% using an injection pressure of 20 bar. The model is in a satisfactory agreement with the tests and itrnalso confirms the experimental trends available in the literature. A parametric analysis on the injection pressure andrntemperature and on the cone spray angle was eventually carried out in order to identify an optimal set of operatingrninjection parameters.