screw, internal gear, compressor, expander, ports
Internally geared positive displacement machines consist of an externally lobed inner rotor rotating inside an internally lobed outer rotor. The rotors can have a constant profile along their length and rotate about parallel axes. Relative to the axis of rotation, the lobes of the rotors can either be straight (as found in conventional gerotor type machines), or helical (as previously proposed by the authors). In either case, the profiles must be specified in order to maintain continuous contact points between the rotors to maintain sealed working chambers. The use of stationary ported plates located at both end faces of the rotors enables periods when fluid is able to enter and leave the machine to be controlled. Shaping of the ports allows compression or expansion to occur within the working chambers formed by the lines of continuous contact between the two rotors. This paper explores the effects of geometrical parameters such as rotor profiles, helical rotor wrap angle and built-in volume ratio, on the isentropic and volumetric efficiency for internally geared machines operating as compressors.