A industrial-scale experimental pipeline with the total length of 258 m and inner diameter of 233 mm was developed to study the thermodynamic properties of pipeline discharge of CO2. Three groups of release experiments with pipeline filled with supercritical CO2 were conducted with three different orifices with diameters of 15 mm

50 mm and full bore individually. Thermocouples were installed on the wall of pipeline to monitor the temperature distributions of the medium inside the pipeline. The characteristics of the phase and density changes and heat transfer processes were studied. Experimental results showed that the pressure and temperature of fluid and the temperature of wall decreased

and eventually became stable in the discharge process. The phase of CO2 was changed from supercritical state to gas-liquid two-phase and finally to gas phase during discharge. It was also obtained that the drop range of temperature was the largest and the intensity of convection heat transfer was the strongest during the initial stage. And the temperature of inner surface of the pipeline decreased more severe and the intensity of convection heat transfer was weaker with the increasing distance from the discharge port. Both the time of discharge and of heat transfer between medium and pipeline became shorter as the orifice diameter decreased. In addition

the temperature gradient between the fluid and the pipe and the intensity of convection heat transfer increased along the direction of pipeline.