Where published:8th International Conference on Compressors and their Systems
Year:2013
Twin screw machines can be used as expanders for variety of applications. This paper describes how the performance of an oil free twin screw air expander of 3/5 lobe configuration was estimated by use of full 3D Computational Fluid Dynamics (CFD) applying a procedure similar to that used for screw compressors. The grid generator SCORG© was employed for pre-processing of the moving domains between the rotors while the stationary grids for the ports were derived from a commercial grid generator. Flow calculations were carried out using the ANSYS CFX® solver. Pressure-angle diagrams, mass flow rates and expansion power at different operating conditions were estimated and compared with experimental test results. The overall performance predictions obtained by simulation agreed very well with measured data. It was concluded that correct design of the high pressure port is vital in order to obtain optimum power output. Leakage flows have a significant effect on screw expander efficiency and have the greatest influence at low speeds and high filling pressures.