An experimental investigation on pressure response and phase transition of supercritical carbon dioxide releases from a small‐scale pipeline

The prediction of the pressure response and phase transition in the event of an accidental carbon dioxide (CO2) release from a ruptured pipeline is of significant importance for understanding the depressurization behaviour and hence the fracture behaviour. This article presented a small‐scale experimental investigation on the pressure response and phase transition of supercritical CO2 release from a pressurized pipeline with a relief orifice. High‐frequency transducers and thermocouples were used to measure the evolution of CO2 pressures and temperatures at different locations after release. The results indicated that pressures at different locations decreased nearly synchronously after release. No vapour bubble and pressure rebound generated in larger scale release experiments were found in our small‐scale release experiments. The depressurization rate was greatly affected by the phase transition. During the release process, the supercritical CO2 firstly turned into an unstable gas with a very great depressurization rate, then changed into the gas–liquid phase with a lower depressurization rate, and finally changed into gaseous CO2. The larger the relief diameter was, the longer the gas–liquid phase state lasted.