New Type Screw Compressor for Helium Refrigerators and Liquefiers

Abstract

In order to meet the recent demand for large scale helium compressors, we have undertaken the development of a scerw compressor of the oil injection type. As a first step in this project, a screw compressor with a capacity of appox. 120Nm3/hr has been constructed and tested. The compressor consists of a compression unit and an oil separation unit. The construction is characterized by a tandem type design, two stages of which are connected hermetically on both sides of the motor. By injection of a considerable amount of oil in the compression process, the following performance characteristics are obtained; a high compression ratio as a single stage and the lowering of discharge gas temperature in contrast to oil free type compressors.Since our screw compressor is of the oil injection type, the reliability of the refrigerator/liquefier system strongly depends on the removal of the oil from the discharge gas. This problem has been solved by the development a special oil separation unit.In a 100hr operational period of the compressor combined with a refrigerator/liquefier, no reduction in the liquefaction rate has been recognized. Results confirm the feasibility of this type of compressor and suggest a direction for further development of large scale screw compressors of the oil injection type.