Objective Aiming at the core scientific challenges of the shock wave-phase transition coupling effect in supersonic carbon capture technology, the purpose is to elucidate the interaction mechanism between CO₂ non-equilibrium condensation and shock wave evolution during natural gas expansion, and to break through the bottlenecks in separator performance optimization.

Method By constructing a numerical model for two-component (CH₄-CO₂) condensing flow, a systematic multi-physical field coupling analysis was carried out, focusing on the evolution patterns of shock waves, the differences in flow models, and the effect of energy recovery efficiency on CO₂ non-equilibrium condensation. Meanwhile, the nonlinear coupling mechanism between the oscillations of thermodynamic parameters and the flow parameters was quantified.

Result In the supersonic flow field, the mixed gas underwent an intense phase transition downstream of the throat after it reached critical subcooling. A large number of condensing nuclei formed at the Wilson point, accompanied by the aggregation of vapor molecules, and the release of latent heat significantly altered the flow field characteristics. Conversely, the temperature spike induced by the formation of a shock wave caused reverse evaporation of droplets, resulting in a dynamic coupling effect between phase transition and supersonic flow. The single-phase flow models had inherent limitations: the predicted shock wave intensity was 54.6% higher than the actual value, the shock wave position lagged by 9.1%, and the cooling capacity and expansion characteristics could not be accurately evaluated. Further research revealed that when energy recovery efficiency increased from 50.0% to 75.0%, the shock wave position moved forward by 39.5%.

Conclusion The critical efficiency thresholds are vital for preventing secondary evaporation prior to droplet separation. Establishing an optimal balance between liquefaction efficiency and energy recovery is essential for practical applications.