VISUALIZATION OF DROPLET ENTRAINMENT GENERATED FROM INTERACTIONS BETWEEN FALLING FILM FLOW AND LATERAL AIR FLOW

摘要

In this study, liquid film breakup was visualized in a 1/20-scaled direct vessel injection system at an APR1400 nuclear power plant in Korea. A film flow with a finite width was formed by the impingement of a water jet directed to the inner surface of a downcomer. The film flow exhibited different wavy surfaces that triggered the breakup based on a sweeping gas flow in a hypothetical nuclear accident. It is difficult to observe droplets in the narrow gap of an annulus because complex two-phase phenomena of the droplets and film flow exist on the surface. In the present study, a shadowgraph method was employed with a hydrophobic coated window, a high-speed camera (2200 fps, 1280 × 800 pixels), and 2-kW halogen lamp to track the breakage of entrainments from the liquid film flow and the movement of liquid droplets. The shadowgraph method with the hydrophobic coating window made it possible to successfully distinguish between the moving droplets in the gas flow and stacked droplets on the surface. The results indicated the distribution of the droplet diameter, mean droplet diameter, mean droplet velocity, and the Weber number at each location on the test section. The adoption of the shadowgraph method with the superhydrophobic coating method allowed successful visualization of droplet entrainment in a narrow gap. This was rarely performed in previous studies. Additionally, meaningful results were obtained for research fields that utilize direct vessel injection systems.