Droplet entrainment by high-speed gas jet into a liquid pool

For the optimal design and safety evaluation of sodium-cooled fast reactors (SFRs), the risk estimation of tube failure in the steam generator (SG) via numerical analysis is very important. This requires the understand of the droplet entrainment behavior induced by high-speed steam injection from the heat transfer tube into the liquid sodium in the shell; however, there is a lack of detailed information such as droplet diameter and velocity due to measurement difficulties. Therefore, this study aims to understand the droplet entrainment caused by high-speed gas injection into a liquid pool and to obtain experimental data for developing proper analysis models. Air was injected into a water pool at various air superficial velocities and the droplets were visualized via the frame-straddling method, obtaining clear images of the droplet generation from the gas–liquid interface. The droplet entrainment was caused by the liquid phase stretching and tearing due to the gas jet shear stress. Based on the visualization results, the droplet diameter and velocity were simultaneously measured at various locations through image processing; the number of fast droplets decreased as the diameter increased. The droplet diameter increased along with the distance from the nozzle. At the center of the jet, the droplet velocity was higher near the nozzle and lower at larger distances. The droplets tended to be larger and slower near the jet interface than near the center of the jet. When the jet interface fluctuation became larger, the droplet diameter increased, while the velocity decreased. Therefore, to develop droplet entrainment analysis models for the risk evaluation of tube failures in SFR SGs, the effect of the jet interface fluctuation on the droplet behavior must be evaluated.