Abstract Cryogenic two-phase turbo-expander becomes a prevalent option in process design of high efficiency cryogenic liquefaction system, especially in modern air separation system and helium system. Computational code of turbine off-design performance prediction in overheated expansion and non-equilibrium condensation module are well established in our former works, as a result, mechanism of nucleation and droplet growth in spontaneous condensation is revealed. However, the predicted off-design performance analysis between single and two-phase expansion as well as wetness influence on turbine performance is not conducted yet. In this study, we investigate a turbo-expander performance analysis in a wide temperature range (Tin=118K∼98K), wetness loss assessment and quantitative calculation in two-phase expansion process. By referring the previous off-design performance of overheated expansion, the two-phase expansion performance under different pressure ratio and rotational speed is researched and compared. According to turbine continuous inlet temperature drop process, the expansion is categorized into three types and their zone boundary is divided. The transitional feature of unexpected change is frequently figured out on the expansion zone boundary, reaction ratio and pressure ratio in diffuser during the continuous inlet temperature drop process is analyzed detailed, which shows the unique and significant role of wetness effect in two-phase expansion. Based on experimental wetness loss assessment method established by Baumann in wet steam turbine, two numerical assessments by using overheated expansion and equilibrium condensation model as reference expansion are carried out and analyzed. To quantitatively analyze the wetness loss influence, efficiency drop caused by wetness and relative wetness loss are calculated by eliminating other component losses in turbine, and the relative wetness loss is fitted with outlet liquid mass fraction mathematically to assist future design of cryogenic two-phase turbo-expander.

中文翻译：

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低温透平膨胀机两相膨胀性能数值研究及失湿定量分析

摘要 低温两相透平膨胀机成为高效低温液化系统工艺设计中的普遍选择，尤其是现代空分系统和氦气系统。过热膨胀和非平衡冷凝模块中涡轮机非设计性能预测的计算代码在我们以前的工作中得到了很好的建立，从而揭示了自发冷凝中的成核和液滴生长机制。然而，尚未进行单相和两相膨胀之间的预测非设计性能分析以及湿度对涡轮机性能的影响。在这项研究中，我们研究了涡轮膨胀机在宽温度范围 (Tin=118K∼98K) 下的性能分析、湿损失评估和两相膨胀过程中的定量计算。参考以往的非设计过热膨胀性能，研究比较了不同压比和转速下的两相膨胀性能。根据汽轮机进口温度连续下降的过程，膨胀分为三种类型，并划分了它们的区域边界。对膨胀区边界上经常发现意外变化的过渡特征，详细分析了进气口连续降温过程中扩压器的反应比和压力比，显示了湿效应在两相膨胀中的独特而显着的作用。基于鲍曼在湿式汽轮机中建立的实验湿损失评估方法，以过热膨胀和平衡冷凝模型为参考膨胀进行了两次数值评估和分析。为定量分析湿损影响，通过剔除汽轮机中的其他部件损失计算湿损引起的效率下降和相对湿损，并将相对湿损与出口液体质量分数进行数学拟合，以协助未来低温两相汽轮机的设计-扩展器。