Compressed air energy storage, Co-rotating scroll machinery, Isothermal compression and expansion, Oil-free, Water injection inside compressor and expander.
The high efficient isothermal reversible machine creates the opportunity to be used as a very efficient small-scale compressed air energy storage (CAES). This new type of CAES links the large-scale smart grid to the decentralized electricity production from renewable sources. In this article is presented an experimental study about a novel oil-free co-rotating scroll machine currently in a prototyping stage. This co-rotating scroll unit does not have a discharge check valve that gives it the possibility to operate as compressor and also in expander mode without any hardware modifications. The distinctive feature of this machine in comparison with an orbiting scroll machine is two mobile involutes working in synchronized co-rotation, one relative to another. The prototype was tested in two experimental test rigs (compressor and expander test rig mode) to determine the viability of the working principle, preliminary performance and also the effect of the water injection on the mechanical power and efficiencies. The experimental results demonstrate that the principle of co-rotating could operate without damage up to a rotational speed of 83.3 Hz in compressor mode (without lubrication). The maximum overall isentropic efficiency obtained from the experimentation in compressor and expander modes were 39 % and 32 %, respectively. The maximum compressor’s volumetric efficiency and expander’s filling factor were 45 % and 2, respectively. The water injection has a positive effect on the performance because it improves the polytropic coefficient and this in turn decreases/increases the power consumption/production of the unit.