U形弯头单元内气液两相流型及压降波动特性

对空气-水两相流在内径16 mm、弯曲半径100 mm的横向U形弯头单元内向上流动时的流型进行了实验研究。利用流动可视化技术及其相应压降波动规律实现了流型的客观识别。总结了不同流型的压降波动特性并据此提出了定量识别流型的新方法。实验范围内发现了分层-搅拌流、塞状-泡状流、段塞-波形流、环状-波形流和环状弥散流等5种与水平直管和垂直直管不同的流型。相比标准偏差，压降波动的功率谱（PSD）分布能更好地反映U形弯头单元内不同流型的流态演变特征与动力学特性。PSD分布的偏度或峰度与气液表观流速比的结合可以定量客观地识别U形弯头单元内的流型，流型转变时的气液表观流速比为1和13。

Flow regimes of gas-liquid two phase flow in a U-bend unit and characteristics of pressure drop fluctuations

Flow regimes of air-water two-phase flow were experimentally studied in a horizontal upward U-bend unit with an inner diameter of 16 mm and a radius of curvature as 100 mm. Visualization technique on flow observation and analysis of corresponding pressure drop fluctuations were used to objectively identify flow regimes. The fluctuation characteristics of pressure drops at various flow regimes were summarized and a new method for recognizing flow regimes quantitatively was proposed. A total of five flow regimes, i.e., stratified-churn, plug-bubble, slug-wavy, annular-wavy and annular-dispersed flows were identified within the scope of experiment. They are different from flow regimes in a horizontal or vertical straight tube. Compared to standard deviation of pressure drop signals, power spectral density (PSD) distributions can better reflect evolution characteristics and dynamic properties of different flow regimes in the U-bend unit. Combination of skewness or kurtosis of PSD distributions and ratio of gas-liquid superficial velocities could objectively and quantitatively identify flow regimes in the U-bend unit. Flow regime transition occurs at ratios of gas-liquid superficial velocities as 1 and 13.