Experiments in downward vertical air-water annular flow in a 26-mm ID, 14-m length pipe were conducted to analyze and improve the understanding of the main characteristics of the liquid film thickness. The downstream evolution of the flow was analyzed at two test sections placed at 90D and 335D from the flow inlet. A non-intrusive conductance sensor and a high-speed camera were deployed to measure the characteristics of the liquid film in the test sections. Thirty-five combinations of superficial air and water velocities were investigated, ranging from 0 m/s to 20 m/s and 0.05 m/s to 0.25 m/s, respectively. The analysis of the liquid film thickness time series provided quantitative features such as the average film thickness, liquid film roughness, velocity, frequency, amplitude, length and the appearance of the disturbance waves. Individual identification of the disturbance waves was performed to investigate the velocity and frequency concerning the distribution of the waves and their interaction. Moreover, variations for all annular flow characteristics were observed in the flow direction and new correlations to estimate the main parameters of the unit wave in DVAF are proposed.

中文翻译：

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垂直向下的气水环流液膜特征：顺流演化与扰动波参数

为了分析和加深对液膜厚度主要特征的理解，在26毫米内径、14米长的管道中进行了向下垂直的空气-水环流实验。在距流动入口 90D 和 335D 的两个测试段处分析了流动的下游演变。部署非侵入式电导传感器和高速摄像机来测量测试段中液膜的特性。研究了 35 种表面空气速度和水速度的组合，范围分别为 0 m/s 至 20 m/s 和 0.05 m/s 至 0.25 m/s。液膜厚度时间序列的分析提供了平均膜厚度、液膜粗糙度、速度、频率、幅度、长度和扰动波的出现等定量特征。对干扰波进行单独识别，以研究波的分布及其相互作用的速度和频率。此外，在流动方向上观察到所有环形流动特性的变化，并提出了估计 DVAF 中单位波主要参数的新相关性。