Effects of initial flow velocity on decompression behaviours of GLE CO₂ upstream and downstream the pipeline

During the transportation of high-pressure liquefied CO2, the CO2 may be in a gas-liquid equilibrium state (GLE) in the pipeline due to the harsh environment or the sudden opening and closing of the source valve. Research on the transient decompression characteristics of CO2 under various conditions is helpful to improve the prediction accuracy of pipeline cracks and the establishment of far-field models of CO(2 )leakage to improve accurate boundary conditions. In this paper, a nonequilibrium liquid-gas phase transition decompression model is established, and the Span-Wagner equation of state (S-W EoS) and Lee model are embedded to accurately predict the thermophysical properties of CO2. Then, the simulation results obtained by the decompression model established in this paper are compared with the experimental data and the prediction results of decompression models used by other scholars for verification. The results showed that the predicted results were in good agreement with the experimental data. Finally, the effects of the initial flow velocity and phase slip on CO2 decompression characteristics are studied. The phase slip has a minor effect on the CO2 transient behaviours, but the initial flow velocity has significant effects on the CO2 decompression characteristics inside and outside the pipeline. In addition, it was found that the decompression wave speed in downstream pipeline was relatively faster, and the pressure plateau value was lower.