Initial Study on the Magnetic Field Characteristics of a Novel Magnetised Air Scroll Expander

Air scroll expanders are increasingly used in energy recovery systems, such as Organic Rankine Cycles (ORC) and compressed air exhaust recovery, and in small scale Compressed Air Energy Storage (CAES) systems. Most of these systems use waste high pressure fluid to drive the expander, which in turn provides mechanical energy directly, or drives a generator. The purpose of this work is to investigate the feasibility of combining the expander and generator into one device by modifying an air scroll expander by inserting magnets and coils into the scrolls and exploiting the relative motion between them to directly generate electricity. The magnetic field generated by the magnets is simulated using Finite Element Analysis (FEA) techniques and a 3D printed prototype. It was found that having multiple magnets in the moving scroll produce a magnetic field with numerous peaks of magnetic flux density. The number, position and size of the peaks were dependent on the number, position, size and polarity of the magnets. The presence of peaks in the magnetic flux indicates that the device could be used to generate electricity with the addition of coils and warrants further investigation.