Numerical and experimental investigation of cryogenic fluid flow characteristics on corrugated packing surfaces

Abstract

Cryogenic distillation is a significant method for producing pure oxygen and nitrogen gas. In the past, due to the high cost and difficulty of conducting cryogenic experiments, the structured packings used in cryogenic distillation are mainly developed and designed by referring to the testing results of room-temperature fluids. The real flow characteristics of cryogenic fluids on structured packings, such as flow pattern and wettability which significantly determines the distillation performance, have seldom been revealed. In this study, with the help of a three-dimensional CFD model and a visual experimental setup, the liquid nitrogen (LN₂) flow characteristics within the geometric unit of a 45° inclined packing element were revealed detailedly under different liquid loads and crimping angles. Comparison studies were also conducted to show the different film flow characteristics between water and LN₂. Additionally, optimization of the crimping angles based on 250Y structured packing was explored. Both simulation and experiment show that the flow pattern and wetting mechanism of the hydraulic test on water are different from those of LN₂ in the actual cryogenic distillation. The LN₂ has much better film flow performance than water due to its different physical properties. In addition, it is found that the crimping angle has a significant effect on the wetting area ratio. For LN₂, the crimping angle of 90° can basically result in a high enough wetting area ratio, while for water, the crimping angle as large as 120° is needed to achieve a high wetting area ratio. It shows that testing and designing the structured packing with water as the main working medium will bring apparent errors in real cryogenic distillation process.