Development of an Efficient Static Shaft Wankel Expander for Organic Rankine Cycles

orc2019 Tracking Number 205

The Organic Rankine Cycle (ORC) presents one suitable solution to the utilisation of low grade heat from some renewables and waste heat from industrial and power generation processes. However, the efficiency of the ORC will be dependent on the efficiency of the expansion device. The Wankel expander shows promise because the disadvantages of the combustion engine are lost when used as an expansion device. Furthermore, it has the advantages of few moving parts, a high power to weight ratio, low noise and vibrations and simplicity in design and manufacture. However, to achieve a good efficiency, an external valve setup is usually required. This paper presents an alternative form of the Wankel expander in which this is not required and the desirable simplicity is maintained. To analyse this expander computational fluid dynamics was utilised. The simulation results gave a maximum isentropic efficiency of 85% (2bar inlet gauge pressure, 6000RPM, 245W). The case with the maximum power gave 572W (3bar inlet gauge pressure, 9600RPM) but only achieved 73% efficiency. The performance of the expander was then compared to other expanders from literature, where it faired comparably in terms of efficiency and as it has greater simplicity, it could be preferred in many applications.