A numerical simulation method for CO2 leakage considering non-equilibrium phase transition

Carbon dioxide (CO 2 ) exhibits high compressibility and complex phase-transition behavior. In the event of a leakage, CO 2 undergoes rapid expansion and intricate phase transitions, resulting in a composite pressure drop process that includes a pressure plateau. Maintaining high-pressure plateau at the outlet supplies energy for the propagation of ductile fractures. Concurrently, throttling effects and phase exchange induce a continuous temperature decrease, which may trigger brittle fracture of the pipeline. Therefore, the establishment of a numerical simulation method capable of accurately predicting the characteristics of CO 2 leakage is of significant necessity. In this work, the SW state equation is employed to calculate the properties of CO 2 . The Mixture and Lee model are integrated to simulate the non-equilibrium phase-transition characteristics. A numerical simulation framework applicable to all phase states of CO 2 depressurization is developed, and experimental data for CO 2 depressurization in gaseous, liquid, and supercritical phases are selected for model validation. The results indicate that this method can effectively simulate the pressure and temperature drop behaviors during the non-equilibrium phase-transition depressurization process of CO 2 leakage across all phase states. For the simulation of pressure and temperature drop, the results obtained for gaseous CO 2 show good agreement with experimental data. However, in the third stage of depressurization, the model predicts a shorter overall depressurization time compared to the experimental observations for liquid and supercritical CO 2 . Additionally, the limiting boundaries of the depressurization path and decompression wave are derived through phase equilibrium calculations and single-phase isentropic depressurization analyses, which further elucidates the non-equilibrium effects in the CO 2 leakage process.