Co-rotating scroll machinery applied to vapor power and vapor compression cycles.

Novel scroll machinery based on co-rotating technology allows to work without internal lubrication both in compression and expansion mode. The main difference between co-rotating and orbiting technology is the presence of two mobile spirals working in synchronized co-rotation instead of having an orbiting and a fixed spiral. As a consequence the co-rotating concept allows to avoid the orbiting inertial forces. This in turn provides higher rotor speeds, thus increased power density and improved volumetric efficiency. This new type of machinery has been designed and tested to be used in the frame of an air energy storage application. In order to demonstrate the machine’s working principle and characterize its preliminary performance an experimental investigation has been performed. A simplified semi-empirical, reduced order model is proposed to predict the performance. This model uses geometrical (displacement and volume ratio) and experimental (electro-mechanical power losses and leak area) parameters and has been calibrated by using experimental data obtained with air as working fluid. Literature proposes different compressor/expander models, however, they are limited by the interaction between oil and working fluid. In oil-free machinery, internal leakages are related only to the leak area, which hardly changes with its operational conditions, hence the leak area is used as fixed parameter to determine the machine’s performance with other working fluids. In this article the prediction of the oil-free machinery performance working as compressor (for vapor compression heat pumps) and as expander (for vapor power cycles) with typical working fluids is presented.