Abstract:

Upon the discharge of supercritical CO₂ pipelines, the medium within the conduit is prone to flashing, thereby exhibiting two-phase flow behavior characterized by phase transition. This intricate process is influenced by a multitude of factors, including non-equilibrium phase change, flow boiling heat transfer, and critical flow dynamics. Under the combined effects of the Joule-Thomson phenomenon and latent heat of phase transformation, the internal environment of the pipeline during the discharge of supercritical CO₂ may encounter low-temperature anomalies, which in turn could precipitate pipeline brittle fracture or the formation of ice blockages. This constitutes one of the pivotal issues constraining the secure discharge of CO₂. This paper provided a comprehensive review of the advancements in understanding the pressure reduction process within pipelines during the discharge of supercritical CO₂, drawing upon experimental research, numerical simulation, and theoretical analysis. It meticulously elucidated the patterns of variation in the phase state, temperature, and pressure of CO₂ within the pipeline throughout this process. The study also critically examined the limitations inherent in current experimental and numerical approaches, identified the salient factors that impacted the formulation of mathematical models for the CO₂ pressure reduction process, and underscored the significant influence of non-equilibrium phase change and flow boiling heat transfer on this process. Furthermore, the study anticipated several critical areas of future research, such as the imperative for high-frequency temperature sensor applications, a comparative analysis of the discharge characteristics of rupture disks versus valves, an investigation into the discharge disparities at various circumferential positions along the pipeline, an in-depth study of the non-homogeneous nucleation and flow boiling heat transfer mechanisms of CO₂, an exploration of the propagation characteristics of pressure reduction waves, the development of two-dimensional flow and heat transfer models for the discharge of supercritical CO₂ pipelines, and the pursuit of relevant engineering application research.

Key words: supercritical CO₂ pipeline, depressurization, numerical simulation, non-equilibrium effect, flow boiling heat transfer

摘要：

超临界CO₂管道泄放时管内介质会发生闪蒸，属于含相变的两相流动行为，这一复杂过程受非平衡相变、流动沸腾传热及临界流动等多因素的影响。在焦耳-汤姆逊效应和相变潜热的作用下，超临界CO₂管道泄放过程中管内可能出现低温问题，会诱发管道脆断或形成冰堵，这是限制CO₂安全泄放的关键问题之一。本文从实验研究、数值模拟和理论分析等角度综述了超临界CO₂管道泄放时管内减压过程的研究进展，系统地梳理了该过程中管内CO₂的相态、温度及压力的变化规律，分析了实验研究和数值模拟中存在的不足之处，归纳了影响建立CO₂减压过程数学模型的关键因素，重点阐述了非平衡相变和流动沸腾传热对该过程的影响，展望了亟待开展的研究内容，包括高频温度传感器应用的必要性、爆破片和阀门泄放的差异性分析、管周向上不同位置泄放的差异性分析、CO₂的非均相成核和流动沸腾传热机理研究、减压波传播特性、超临界CO₂管道泄放二维流动与传热模型以及相关工程应用研究。

关键词: 超临界CO₂管道, 减压, 数值模拟, 非平衡效应, 流动沸腾传热