The impact of a bilateral symmetric discharge structure on the performance of a scroll expander for ORC power generation system

Scroll expander is a good candidate for small-scale ORC systems. Discharge flow has a significant impact on the expander performance. In this study, a novel bilateral symmetric discharge structure for scroll expander was proposed and compared with the unilateral discharge structure using CFD approach. Discharge flow features and the performances of the scroll expander were analyzed. Results show that the pulsation of the discharge mass flow rate in the expander with bilateral discharge structure is related to both the eccentric rotation of the orbiting scroll and the decompression drainage of the second discharge port. The symmetric discharge structure contributes to the pressure reduction and the uniform flow in working chambers. Both pressure distortions and secondary flows are weakened or even eliminated. Special damped pulsation of pressure in discharge chamber is also revealed, which has an important impact on the driving moments of the scroll segments in discharge chambers. The pulsating pressures in discharge chambers vary in an opposite peak-valley pattern. The symmetric discharge structure could balance the pressure pulsation level between discharge chambers and enhance the driving moment by 6.38%. The driving moment increment of the scroll segments between symmetric working chambers plays a positive role in the expander performance.