超临界CO_2管道减压过程中的热力学特性

Thermodynamic properties during depressurization process of supercritical CO_2 pipeline

基于工业规模CO_2管道(长258 m,内径233 mm)实验装置开展了3组不同泄放口径的超临界CO_2的泄放实验,测量了CO_2减压过程中管内介质压力变化以及介质与管壁的温度分布,分析了减压过程中CO_2相态、密度变化及管壁内外传热过程。研究表明,超临界CO_2泄放导致管内介质压力、温度及管壁温度均下降,最终趋于稳定,介质由超临界相变为气液两相最终变为气相。初始阶段的温降幅度最大,对流换热强度最大。距离泄放端越远,管内顶部和底部介质的温降幅度越大,对流换热强度越小,在泄漏口附近的对流换热最为剧烈。随着泄放口径的变大,泄放时间和管道内介质与管道的换热时间都变小,且沿着管道方向的管道内流体和管壁的温度梯度变大,对流换热强度也变大。

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.