Abstract The distillation efficiency of the cryogenic air separation unit is significantly affected by the inside flow performance of the cryogenic oxygen and nitrogen mixture in the structured packing. Owing to the difficulties in cryogenic experiments, the development of structured packings in cryogenic distillation often relies on the hydraulic experiments at room temperatures, while the real flow characteristics of the cryogenic fluids in the structured packing are hardly known. In this work, with the help of CFD simulation, a 3-D model combining VOF method was built to study the flow characteristics of liquid oxygen (LOX) in the structured packing, and comparisons with water were also carried out. Effects of liquid load and equivalent contact angle on the flow patterns, the liquid hold-up, the interfacial area and the average film thickness were analyzed. Results show that the flow of water is mainly rivulets, while LOX can form film flow on the packing surface in a large fluid load range due to its small contact angle and surface tension. Because the interfacial area of LOX isn’t strongly affected by liquid load, its liquid film thickness could be the main consideration for heat transfer, mass transfer and load selection. Since the variation of contact angle has slight effect on the flow parameters of LOX, the optimization of structured packings for cryogenic distillation may not be expected by the surface micro texture improvements.

中文翻译：

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规整填料中液氧和水流动特性的数值研究

摘要 低温空分装置的蒸馏效率受规整填料中低温氧氮混合物内流性能的显着影响。由于低温实验的困难，低温蒸馏规整填料的开发往往依赖于常温下的水力实验，而低温流体在规整填料中的真实流动特性鲜为人知。在这项工作中，借助 CFD 模拟，建立了结合 VOF 方法的 3-D 模型，研究了规整填料中液氧 (LOX) 的流动特性，并与水进行了比较。液体负载和等效接触角对流动模式、持液率、分析了界面面积和平均膜厚。结果表明，水的流动主要是小溪，而LOX由于其接触角和表面张力小，可以在较大的流体载荷范围内在填料表面形成薄膜流动。由于液氧的界面面积不受液体载荷的强烈影响，其液膜厚度可能是传热、传质和载荷选择的主要考虑因素。由于接触角的变化对液氧流动参数的影响很小，因此表面微结构的改善可能无法预期用于低温蒸馏的规整填料的优化。由于液氧的界面面积不受液体载荷的强烈影响，其液膜厚度可能是传热、传质和载荷选择的主要考虑因素。由于接触角的变化对液氧流动参数的影响很小，因此表面微结构的改善可能无法预期用于低温蒸馏的规整填料的优化。由于液氧的界面面积不受液体载荷的强烈影响，其液膜厚度可能是传热、传质和载荷选择的主要考虑因素。由于接触角的变化对液氧流动参数的影响很小，因此表面微结构的改善可能无法预期用于低温蒸馏的规整填料的优化。