Numerical and experimental investigation of static shaft Wankel expander for compressed-air energy storage

Compressed air energy storage (CAES) is a promising technology for storing mechanical and electrical energy using the gas power cycle. The expansion device is a critical component of the CAES that determines the overall performance of the system. Standard Wankel expander (SWE) is one of the volumetric expanders which has several advantages including low vibration, ability to produce high power output, low manufacturing cost and less moving parts. However, SWE requires valves for timing the inlet and outlet flow and a balancing system to ensure reliable operation. Static shaft Wankel expander (SSWE) is an attractive solution to enable valves' removal and the need for balancing system. This paper presents a detailed experimental and numerical investigation of an SSWE performance at various operating pressures and temperatures for CAES application. An advanced computational fluid dynamic simulation model taking into account the dynamic motion of the SSWE and utilising real gas air properties. A compressed air test rig was constructed and instrumented with temperature, flow rate, pressure and torque sensors. Experimental testing at temperatures 20 degrees C to 80 degrees C and pressures of 1.5 bara to 3 bara was conducted and compared to the CFD simulations results. Correlations were developed for the friction power loss. Experimental results showed that the developed SSWE can produce power output of 504 W at 80 degrees C and 3 bara and its isentropic efficiency reached 71 % at 60 degrees C and 2 bara.