Influence of rotor geometry on tip leakage and port flow areas in gerotor-type twin screw compressors

Abstract

Conventional twin-screw compressors are positive displacement machines that form working chambers between two helical, parallel rotors and an outer casing. This study investigates an alternative configuration of rotors for compressor applications, in which the working chambers are formed by continuous contact between meshing inner an outer rotors. This is a similar configuration to gerotor machines, which are commonly used in fuel and oil pumping applications and as hydraulic motors. For compressor applications, the use of helical rotors with appropriate porting in a gerotor-type configuration has been identified as having potentially lower rotor contact forces and larger port areas than occur with non-helical rotors. This study investigates how key performance parameters of a gerotor-type screw compressor (volume, port flow areas and tip leakage areas) are influenced by the profile, dimensions and wrap angle of the rotors. The results of this geometric analysis are compared with a conventional twin-screw compressor, and suggest that the gerotor-type screw compressor can achieve higher axial port areas and lower tip leakage area over most of the compression cycle.