Study and Design of Helium Scroll Compressor

Abstract

Scroll compressors are orbiting positive displacement compressor. A Copeland scroll compressor of 7.5 KW R410A refrigerant is converted to helium based scroll compressor. Normally the refrigerants used in the scroll, screw or reciprocating type have low Y (gamma) value, so the heat of compression is low. When helium gas is used due to its high Y value of 1.67, it generates high grade of compression heat. Moreover, in cryogenics application, the amount of oil carryover to the systems is not permitted with the compressed helium gas from scroll compressor as in this case, it will make the system run out of order. In refrigerant cycle, we allow the oil to pass with refrigerant which in cryogenics application is kept below 0.1ppm level. In this Copeland scroll compressor the suction pressure to be maintained at 6 bar and the discharge pressure to be maintained at 21 bar, thus giving 3.5 pressure ratio across the scroll compressor. Since at the discharge of scroll compressor it contains helium gas with some oil impurities , so proper oil filters are installed which will bring down the oil impurities from the compressed gas to below 0.1 ppm. For the cooling purpose of the compressed helium gas and oil, an aftercooler has been used. The aftercooler is an air cooled tube fin heat exchanger type. For cooling the oil inside the compressor, the oil needs to be drained out and be cooled down in a plate heat exchanger. After cooling down of oil, it is fed back to the compressor through an gear oil pump. The study of modified helium compressor from R410A scroll compressor and basic design of this modified helium compressor is done.