Characteristics of vertically falling liquid film affected by cross gas flow in a narrow flat channel

Gas crossflow on a falling liquid film occurs in many practical cases in industries, particularly, in the downcomer of the APR1400, when accidents such as damage to the cold legs occur, hot steam crossflows over the vertical falling water film formed by the water impingement on the wall through a direct-vessel injection nozzle. Such crossflow may degrade the heat transfer ability of the liquid film. To investigate the film characteristics of downward flowing water, across which air was blowing horizontally, an experimental setup was designed and assembled. Experiments were conducted under different water flow rates (2, 3, 4, and 5 L/min) and different air velocities (0, 3.4, 4.9, 6.9, 8.4, and 9.8 m/s) to determine their effect on the film structure. A confocal chromatic sensor was employed to detect film thickness, film width, and wave amplitude. It was found that the base film thickness and wave amplitude do not vary when superficial air velocity is not larger than 4.9 m/s. As air velocity increases, the base film thickness exhibits a decreasing trend and wave amplitude exhibits an increasing trend. In particular, wave amplitude shows a different tendency from that found in annular flow. Moreover, local base film thickness and wave amplitude decreased and increased along the film flowing direction, respectively. Furthermore, the average film thickness was found constant throughout the whole air velocity range. In addition, film width expanded nonlinearly as the water flow rate increased, and the slope of the film centerline under different superficial gas velocities was presented for the first time.