Transporting massive quantities of carbon dioxide through a pipeline in its supercritical state is extremely convenient. Because of the unique properties of supercritical carbon dioxide, however, leakage occurring in such conditions can be extremely intricate, resulting in the dispersion area following leakage being influenced by numerous factors. In this study, this problem is addressed in the frame of the so-called Unified Dispersion Model (UDM), and various influential parameters are considered, namely, leakage pressure, leakage temperature, leakage aperture, leakage angle, atmospheric stability, wind speed, and surface roughness. The results show that the supercritical carbon dioxide dispersion is primarily influenced by high air temperatures, low wind speeds, reduced surface roughness, and release temperatures slightly below the critical temperature. Additionally, leak apertures also contribute to the dispersion. The dispersion is maximized under atmospheric stable D conditions, and when the leakage angle is 0°, the farthest downwind distance is 10 times greater than that at a leakage angle of 90° under the same conditions.

Gas-liquid flow (GLF), especially slug and annular flows in oil and gas gathering and transportation pipelines, become particularly complex inside elbows and can easily exacerbate pipeline corrosion and damage. In this study, FLUENT was used to conduct 3D simulations of slug and annular flow in elbows for different velocities to assess the ensuing changes in terms of pressure. In particular, the multifluid VOF (Volume of Fraction) model was chosen. The results indicate that under both slug and annular flow conditions, the pressure inside the elbow is lower than the outside. As the superficial velocity of liquid and gas increase, the pressure and liquid flow velocity at different positions of the elbow also increase, while the secondary flow weakens. Under annular flow conditions, the liquid film on the outer side of the elbow is thicker than that on the inner side, and the liquid velocity in the main liquid film zone is the lowest.