Steady and dynamic performance of CO₂ in a labyrinth channel: Effects of thermophysical properties on energy conversion, flow capability, and instability

The multi-stage labyrinth control valves in supercritical CO₂ Brayton cycle (SCBC) system need to accommodate multiple operating conditions, including transcritical, subcritical, and supercritical states, with its internal flow parameters continuously evolving in response to system transients. However, the highly nonlinear thermophysical property variations of S-CO₂ in the near-critical region pose significant challenges for the valve operation stability during high-decompression throttling and adverse impact SCBC dynamic regulation. To address this issue, systematic experiments on steady-state and dynamic operating characteristics were conducted to investigate the influence mechanisms of CO₂ thermophysical properties on energy dissipation, flow capability, and flow instability. Experimental results reveal that under transcritical conditions, CO₂ exhibits the highest flow capacity, but is accompanied by pronounced nonlinear property variations, resulting in the maximum amplitude of flow pressure fluctuation and significant flow instability. In contrast, supercritical conditions demonstrate superior dynamic robustness, with substantially reduced pressure oscillation amplitude and regulation time under flow step disturbances. This study elucidates the regulation mechanisms of CO₂ thermodynamic states on the flow characteristics and dynamic stability of labyrinth channels, identifies the optimal operating range for labyrinth control valves, and provides crucial experimental evidence and theoretical guidance for dynamic control optimization of SCBC systems.