A thermal flash-boiling model for secondary atomization of Lagrangian droplets

Flash-boiling occurs when super-heated liquid are injected in an environment whose thermodynamic conditions are below the saturation level. In combustion devices, this phenomena can be helpful to obtain a rapid vaporization of the fuel immediately after the injection. From the modeling standpoint, flash-boiling breakup is interpreted as a sequence of events that can be heuristically modeled. This manuscript aims at proposing an heuristic model that involves nucleation of multiple bubbles inside the droplet and their thermally-driven growth. The a priori validation shows that the Blander and Katz nucleation model with the full chemical potential decently predict the nucleation temperature in an ammonia droplet and the Mikic growth model coupled with a proposed temperature equation for the internal heat transfer captures the bubble radius growth of different water bubbles. From a simulation of an ammonia droplet explosion with OpenFOAM, the children droplet temperature is also well predicted. The time scales analysis revealed the region of applicability of the model, allowing a consistent reduction of computational cost.