Atomization mechanisms of a wall-impinging jet in a shallow pool

Atomization of a liquid jet in an immiscible liquid-liquid system is essential for maintaining safety in the nuclear industry. The Japan Atomic Energy Agency has developed a method to evaluate the behavior of molten fuel entering a shallow coolant pool using numerical and experimental simulations in an immiscible liquid-liquid system, focusing on hydrodynamic interaction between the fuel and pool. However, the atomization behavior associated with the spreading of the wall-impinging liquid jet immediately after entering a shallow pool in the system is quite different from jet-breakup regimes in a deep pool, and there are a few reports. Such atomization behavior can change subsequences in severe accidents in the nuclear industry, and the investigation of the atomization behavior of the wall-impinging liquid jet is significant. Herein, we investigate the atomization behavior of a wall-impinging liquid jet in terms of droplet formation and its flow field using numerical simulation and a dispersed-phase tracking method. The results show that the atomization behavior comprises droplet formation with three patterns. We obtain droplet properties immediately after droplet formation and develop theoretical boundaries enclosing two regions for droplet formation using dimensionless numbers. We characterize the patterns by comparing them with the theoretical regions and elucidate the droplet formation mechanisms of each source. Moreover, we establish the relationship between droplet formation as the local behavior and atomization as the whole behavior of the jet. Thus, this paper clarifies the atomization mechanisms in the liquid film flow of the wall-impinging liquid jet in a shallow pool.