Computationally-Derived Submodel for Thermally-Induced Secondary Atomization

Thermally-induced secondary atomization (TISA) enables enhanced atomization, better mixing and faster evaporation in multi-component sprays. Despite its importance in a number of applications, TISA is not yet well understood. In this work we study numerically the e ﬀ ects of key physical parameters on TISA dynamics, with particular emphasis on breakup. To this end, we simulated a series of cases for suspended droplets in microgravity conditions, varying the number of bubbles near the liquid-gas interface. We performed a total of 800 simulations with di ﬀ erent ﬂuid properties investigating a wide hyperspace. In particular, we varied viscosity, surface tension, number and size of bubbles, as well as the droplet size, identifying two main parameters necessary for modelling purposes: the breakup time, τ b , and maximum normalized surface area, S f . Here we deﬁned the breakup time as the time between the beginning of the simulation and the maximum surface area observed. We also calculated the Pearson’s coe ﬃ cient to estimate the inﬂuence of each variable on the parameters of interest, understanding that the size of the largest bubble controlled S f while the Ohnesorge number strongly inﬂuenced τ b . We further employed the dataset to formulate simple mathematical correlations for S f and τ b by performing a multi-variable regression. Moreover, we looked into the dynamics of the secondary droplets generated by the process, demonstrating that the velocity and size of the ejected droplets are linked to the size of the bubbles that generate them.