A Thermodynamic Chamber Modelling Approach for Oil Free and Oil Injected Twin Screw Compressors

As computational modelling becomes an increasingly reliable and key component in accelerating the design process for twin screw machines, the goals for engineers now include developing faster running and physically accurate component models to optimize machine performance and efficiency, minimize internal leakage, reduce unwanted noise and pulsations, and properly size bearing supports in the machine. Accurately capturing these aspects via physical models helps in analyzing operating points that were not tested as well as in understanding how the machine will perform in a surrounding system. Thereafter, engineers can find an optimal design in a timely manner for the fastest speed to market as well as reduce physical testing to keep development costs low. This paper presents the use of a multi-physics modelling platform – GT-SUITE – in conjunction with SCORG – a well-established tool for the design and analysis of twin screw machines – to explore meeting the aforementioned goals. Two case studies are presented for a 3/5 oil free air compressor and a 4/5 oil injected air compressor. Comparisons to the mass flow rates of the gas and oil, temperatures, indicated power and the instantaneous chamber pressure vs rotation angle were made against test data available from the Centre for Compressor Technology at City University. The sensitivity of oil injection timing on the discharge temperature and power is shown and an optimum timing was found. The validated chamber models may be integrated into a system as well as used for further optimization to improve the original compressor performance.