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 \textit{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.