Dry screw compressor are limited to maximum pressure ratios of approximately 3: 1 due to the high gas temperatures resulting from the compression process, which cause them to deform To attain higher pressure ratios the compressors must be cooled. The main features of heat transfer in screw compressors are reviewed qualitatively and resulting from this, an analytical and experimental study was carried out to validate a novel but simple means of rotor cooling, involving local injection of very small amounts of a volatile liquid. It is shown that this enables oil free compressors to operate up to much higher gas temperatures and hence, extends the pressure ratio over which a single oil free screw compressor stage can operate.
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