Dynamic characteristics analysis of supercritical CO2 power cycle under system volume effects

Developing an accurate system-level transient model for the recompression supercritical CO₂ power cycle is essential for understanding its dynamic behavior and enhancing operational efficiency. While prior research has extensively addressed the modeling of heat exchangers and turbomachinery, the dynamic impact of system cavities, such as heat exchanger casings and interconnecting pipes, has been largely neglected. This study introduces a comprehensive dynamic system-level model developed in Modelica language, which uniquely incorporating lumped parameter cavity modules to evaluate the impact of cavity volume and location on system performance. By systematically varying the volumes and positions of eight representative cavities, the analysis reveals that the five cavities from the turbine outlet to the main compressor inlet consistently enhance thermal efficiency, while the remaining three cavities from the recompressor outlet to the turbine inlet reduce thermal efficiency but shorten stabilization times. Specifically, the cavity between the low-temperature recuperator and the cooler increases thermal efficiency by 0.23 % at 40 % load, while the cavity between the low- and high-temperature recuperators shortens recovery time by 10 s. These results highlight the previously underappreciated role of cavity dynamics in closed-loop, single-phase systems like the supercritical CO₂ cycle. This work provides new insights into the transient characteristics of such systems and offers a foundation for improving system design, control strategies, and the reliability of supercritical CO₂ power technologies.