Features of the liquid film in downward vertical air-water annular flow: downstream flow evolution and disturbance wave parameters

Abstract

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.