大带液率低温两相透平膨胀机的基础问题研究

Being the core-block of air separation plants and gas separation and liquefaction systems, turbo-expanders should definitely be responsible for the most part of refrigeration capacity for the whole cryogenic system. The feasibility and economy of the whole cryogenic equipment can be prompted by achieving two-phase flow state at the outlet of the turbo-expander. This project aims on the most basic and core issues in the expansion process of the cryogenic turbo-expander working under high liquid fraction condition. An pioneering investigation into the mechanism of phase change and energy transformation, and the optimal design method will be carried out to proclaim the mechanism and law for the unsteady condensation and nucleation in the expansion process, and to describe the whole nucleation process of the near Mach number two-phase expansion and the characteristics in the process of phase separation in rotating flow passages. The main objectives of this project aim to figure out the bottle neck of the two-phase cryogenic turbo-expander high-efficiency operation in high liquid fraction condition. Moreover, the numerical model will be set up to simulate the flow passages of the two-phase turbo-expander which has significance for finding out the influencing factors of unsteady running resulted from complex fluid flow and changes of the working condition. The results from this project will be the foundation for the further investigation of two-phase cryogenic turbo-expander working under high liquid fraction, and will also make contributions to the basic scientific research in cryogen non-equilibrium thermodynamics, compressible fluid two-phase flow, and to the research of the two-phase expansion, energy conversion and aerodynamic performance of high speed turbo-machinery.

透平膨胀机是低温系统中主要的冷量来源，也是现代空分装置和低温液化系统中的核心部件。透平膨胀机出口达到两相状态可提供更多的冷量，提高整套低温装置的可行性与经济性。针对低温透平膨胀机带液膨胀的核心基础问题，拟对大带液率低温两相透平膨胀机流动相变与能量转换机理及设计技术进行开拓性探索，揭示低温工质（空气）膨胀凝结成核的机理及规律，描述旋转流道内近马赫数低温膨胀相变过程以及液滴发展和相态分离特性，最终解决低温两相透平膨胀机设计计算与高效运行的瓶颈问题。并针对大带液率低温两相透平膨胀机内部的混合工质非稳态相变流动，高速旋转机械流道效应、液滴冲击以及非稳定工况，对膨胀机通流单元进行数学建模与耦合数值分析，获得低温两相膨胀机性能预测和设计与仿真正反两方面命题求解。本项目将为低温两相透平膨胀机的进一步研究提供基础，也将为低温工质非平衡热力学两相流动及高速离心机械两相膨胀能量转换机理和气动性能研究做出贡献。

由于透平膨胀机出口达到两相状态时可提供更多的冷量，针对低温透平膨胀机带液膨胀的核心基础问题，本项目目标要求的研究内容为：1. 研究低温工质（空气）非稳态非平衡相变瞬态界面形成机理；2. 研究低温工质近马赫数两相流体在叶轮中的膨胀特性以及非平衡态流体高速流动降压自发凝结现象；3. 研究大带液率低温两相透平膨胀机流道设计方法、性能预测与动态仿真。.本项目针对大带液率低温两相透平膨胀机的基础问题研究，基于不可逆过程热力学和非平衡热力学理论，揭示了空气降压（过冷）凝结高速膨胀过程中凝结核的形成、相变界面发展，气液两相间的物质与能量交换，非均匀流动模型及流型转换的机理，解决了低温工质过饱和（过冷）膨胀高速流动凝结相变、成核、发展与两相流动的基础问题；建立了高速旋转流道内近马赫数两相膨胀（过冷）凝结与发展过程及其定量描述的数学模型，分析了叶轮中低温两相流动流型与气液比例、相态分布与离散特征，揭示了三维叶片扭曲流道中空气近马赫数膨胀两相流动与能量迁移的内在联系，获得了大带液率透平膨胀机的损失组成、叶型选择、液滴形成及其运动规律以及边界效应、相间滑移、三元流动与两相流型和液滴冲击对部件性能的影响，掌握了低温两相透平膨胀机设计与性能分析的基础理论；在理论分析和数值模拟工作的基础上，根据分析结果设计试制了大带液率两相膨胀机叶轮，开展了低温两相透平膨胀机气动性能和系统匹配实验，获得了透平进出口温度、压力、湿度等参数，利用修正后的成核模型完成模拟，并与实验测得的基础数据进行对比，进一步改进和完善了数理模型，从而更好的指导了叶片型线设计以适用于带液透平的高效运行。最终通过对实验结果的分析与归纳，验证了理论研究的正确性，并对理论模型和仿真预测方法进行了改进，设计了大带液率两相膨胀叶轮；开展了大带液率低温两相透平膨胀机的实验测试；掌握了大带液率低温两相透平膨胀机的基础理论和关键技术。