Application of a generalized compressor modeling framework for simulating an oil-injected twin-screw compressor

Oil-injected twin-screw compressors are widely employed in many commercial and industrial applications because of their high efficiency and reliability. Although extensive literature on modeling techniques applied to twin-screw machines exists, researchers are continuously developing models to capture advanced physical phenomena occurring during the compression process (e.g., mass and heat transfer mechanisms). In order to generalize the concept of mechanistic compressor modeling, a framework for the simulation of positive displacement compressors and expanders (PDSim) has been developed and validated by the authors. The platform has been utilized to model a number of compressor types including scroll, reciprocating, linear, single-screw, rolling-piston, Z, and spool. In this work, the simulation tool has been extended to include twin-screw machines. Beside the detailed geometry model needed to obtain volume curves of the working chambers, sealing lines, and rotor surface areas, three main aspects have been enhanced with respect to the existing literature: (i) a two-fluid (refrigerant and lubricant oil) chamber model with mass and heat transfer interactions; (ii) computation of gas forces, loads on the bearings, and hydrodynamic bearing sub-models; (iii) detailed overall energy balance with a multi-lumped temperature thermal network and a discharge gas pulsations post-processing model. A 4/6 oil-injected twin-screw compressor has been considered to conduct experimental analyses with internal pressure and force sensors, modeling and validation as well as sensitivity analyses.