Flow Loss Mechanisms Investigation on a Novel Corotating Scroll Expander for Supercritical Carbon Dioxide Power System

The expander is the critical component of supercritical CO2 (S-CO2) Brayton cycle power generation systems. The paper proposed an innovative design for a high-speed co-rotating scroll expander and created a 3D CFD transient simulation model to investigate its flow characteristics and loss mechanisms. Entropy production theory and omega vortex identification method were utilized to analyze the primary regions and causes of flow losses during different working processes of the co-rotating scroll expander. The results showed that flow losses of the co-rotating expander mainly occurred during the suction and discharge processes. During the suction process, the disturbance by the two scroll tips resulted in prominent vortex structures, leading to significant irreversible losses. During the expansion process, the fluid flow in the expansion chamber is relatively stable due to the synchronous and co-directional rotation of the two scrolls, resulting in only small irreversible losses. During the discharge process, separated flow at the area behind the scroll tails, mixing working fluids between the discharge and back pressure chamber, caused substantial irreversible losses. The study provided theoretical guidance for optimizing flow control in the co-rotating scroll expander used in S-CO2 Brayton cycle power generation systems.