Reciprocating Compressor, OCR, ODR, CO2
In addition to the gaseous refrigerant an oil-lubricated reciprocating compressor also transports a certain amount of oil into the refrigeration circuit. The amount of oil carried out of the compressor is dependent on the operating conditions and the internal compressor design but is usually assumed to be in the range of a few mass percent. With respect to installation costs, reliability and efficiency of the whole refrigeration system the oil circulation ratio (OCR) should be kept as low as possible. In order to get a better understanding on how oil is transported inside a reciprocating compressor for CO2 applications, the internal flow pattern was analyzed and possible oil transport mechanisms were investigated. The compressor was therefore divided into different subsections. Based on these subsections experimental studies on the potential of each individual oil transport mechanism were carried out. In order to measure the OCR at different operating conditions a new test rig for CO2 compressors was built up. The internal design of the tested compressor as well as the test setup were gradually modified to allow the separate investigation of the different subsections and thus the potential of the oil transport mechanisms on reducing the overall OCR. The measurements clearly identified the oil transport mechanisms and gave indications for further reduction of OCR in reciprocating compressors.