通过管道对液态CO₂进行输送或泄放到大气中的情况在消防和工业领域中非常普遍，然而，由于CO₂物性特殊，在大压降和大流量条件下，常引发管道结冰堵塞、断裂、窒息、冲击和冻伤等风险。带压管道或容器安全评估的核心是能准确预测其内部流动参数的变化规律，同时液态CO₂的安全输送和安全泄放与CO₂流动阻力和射流特性又密切相关，因此准确掌握CO₂两相流动管路阻力和射流特性，构建数学模型量化其输送和泄放过程的关键参数变化，这对CO₂管道系统的安全设计和事故后果预测至关重要。

本文设计和搭建了CO₂管路流动阻力特性和射流冲击特性实验装置，采用实验、数学模型和模拟的方法研究液态CO₂两相流动管路阻力和喷射特性，具体工作包括：

研究了喷嘴孔径的改变对CO₂传输特性（压力、温度和质量流量）的影响，并且基于液态CO₂的闪蒸延迟现象对传统的HEM（Homogenous Equilibrium Model）进行了修正，并假设延迟的液/气转变跟压降大小有关，发现改进后的模型在预测管道压降，尤其是大压力梯度下的延迟液/气转变方面具有良好的准确性。通过模型分析了等效粗糙度、质量流量、环境温度和海拔对压降的影响，还发现随着初始压力从2～7 MPa的增加，压降先升高后降低，因为在这个范围内均相CO₂的密度有一个极值。

研究了喷嘴孔径、初始压力和冲击距离的改变对CO₂射流特性（羽流结构、质量流量、冲击温度和冲击力）的影响。基于HEM假设构建了气-液两相等熵膨胀射流模型，并且该模型对射流流量的预测具有良好的准确性。分析模型计算结果发现，初始CO₂流动状态和物性参数共同决定出口质量通量和出口压力，而喷嘴孔径只是改变了流通面积大小。还发现由于喷嘴出口处液态CO₂的快速闪蒸会导致射流速度急剧增大，基于动量假设的冲击力计算结果与实验结果相差甚远。

建立了考虑实际气体状态方程的可压缩两相CO₂射流CFD（Computational Fluid Dynamics）模型，并采用欧拉Mixture多相流模型对CO₂喷嘴射流进行模拟研究，将有限实验结果对仿真模拟结果进行了可靠性验证，还对模型的计算结果进行了分析。

论文研究成果可为CO₂管道系统的安全设计和优化运行提供理论基础和数据支撑。

The transportation of liquid CO₂ through pipelines or directly released into the atmosphere is very common in fire protection and industrial fields. However, due to the special physical properties of CO₂, under the conditions of large pressure drop and large flow often lead to pipeline freezing and blockage, risk of breakage, suffocation, shock and frostbite. The core of the safety assessment of a pressurized pipeline or container is to accurately predict the change law of its internal flow parameters. At the same time, the safe transportation and discharge of liquid CO₂ are closely related to the CO₂ flow resistance and jet characteristics. Therefore, accurately grasping the pipeline resistance and jet characteristics of CO₂ two-phase flow, and building a mathematical model to quantify the changes of key parameters in the transportation and release process are crucial to the safety design and consequences prediction of the CO₂ pipeline system.

In this paper, both experimental devices for CO₂ pipeline flow resistance and nozzle jet characteristics were designed and built, and the experiments, mathematical models and simulation methods were used to study the resistance and jet characteristics of liquid CO₂ two-phase flow. The main works include:

The CO₂ transport characteristics of different nozzle sizes were experimentally studied (including pressure, temperature and mass flow rate), and a modified HEM (Homogenous Equilibrium Model) was built to simulate the pressure drop behaviour considering the flashing delay phenomenon, assuming that the delayed liquid/vapour transition was related to the pressure drop, and the modified model has good accuracy for predicting pipe pressure drop, especially the delayed liquid/vapour transition under large pressure gradients. This model was also used to analyze the effects of equivalent roughness, mass flow, ambient temperature and elevation on the pressure drop, and it was found that with the increase of the initial pressure from 2 to 7 MPa, the pressure drop first increased and then decreased, because there is a density peak in this range.

The CO₂ jet characteristics of different nozzle sizes, initial pressure and impact distance were experimentally studied (including jet structure, mass flow, impact temperature and impact force). A gas-liquid two-phase isentropic expansion jet model was built which based on HEM assumption, and this model has good accuracy for predicting the jet of mass flow rate. The model calculation results show that the initial CO₂ flow and physical parameters determine the jet mass flux and outlet pressure, while the nozzle size could only change the flow area. It is also found that the rapid flashing of liquid CO₂ at the nozzle outlet will increase the jet velocity. The force calculated results based on the momentum assumption are far from the experimental results.

A two-phase CO₂ jet CFD (Computational Fluid Dynamics) model considering the real gas behavior was developed, and the Euler mixture multiphase flow model was used to simulate the CO₂ nozzle jet, and the reliability of the simulation results was verified by the limited experimental results, and the CFD calculation result were analyzed.

The research results of this paper can provide theoretical basis and data support for the safe design and optimal operation of CO₂ pipeline systems.

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