Influence of Bearing and Seal Design on Performance of an Oil-Injected Screw Compressor for Refrigeration Applications

Screw compressors are key components in a range of refrigeration and air conditioning applications. It is essential that the design and operation of these systems is optimised to ensure energy efficiency and reliability. An important aspect of the compressor design is the choice of bearings used to support the twin helical rotors. These bearings must be capable of providing the reaction forces required to accurately locate the rotors across a defined range of inlet and discharge pressures for machines with a range of volume ratios and operating speeds. This paper explores the selection process for both rolling element and hydrodynamic bearings. The influence on compressor performance of these bearings can be defined in terms of the frictional power losses and required oil supply flow rates. Bearings can also have indirect influence on overall compressor efficiency, due to the potential introduction of leakage paths of process gas through low-pressure bearing oil drains. Therefore, additional sealing requirements for each bearing type are investigated, allowing an assessment of leakage flow and frictional power loss of bearing/seal systems and their influence on the overall performance of different compressor configurations in terms of energy efficiency, lifespan and maintenance requirements.