twin-screw compressor, variable lead, multi-chamber simulation, geometry variation, efficiency optimization
The paper deals with a theoretical investigation of screw machines applied as refrigerant compressors, focusing on the compression process. The refrigerant used is R227ea with a pressure ratio of four. A wide range of geometric parameters such as rotor length, internal volume ratio and wrap angle are varied in order to show their influence on efficiency, with a view to finding out how energy conversion can be improved by using dual lead rotors. These rotors possess two segments with different rotor lead in order to optimize the progression of chamber volume, clearance size and outlet area. The rotor profile under investigation is an asymmetric SRM profile whereas the diameter of the male rotor as well as the clearance heights remain constant throughout the simulation. The impact of the machine geometry on efficiency is examined by performing a multi-chamber simulation. The improvement in energy conversion that can be achieved by using a dual lead is quantified in terms of isentropic efficiency and delivery rate. Especially for greater length-to-diameter ratios, benefits in efficiency and mass flow rate may be expected.