Impact, spreading dynamics, and evaporation of ammonium perchlorate aqueous solution droplets on a heated surface

The impact and evaporation of ammonium perchlorate (AP) aqueous solution droplets on heated surfaces are experimentally studied, with a focus on the influence of surface temperature, Weber number, and AP mass concentration. High-speed imaging is employed to record the droplet spreading, retraction, and boiling behaviors, revealing five distinct impact regimes: deposition, partial rebound, secondary atomization, explosive rebound, and jet ejection. The results revealed that both surface temperature and Weber number enhance droplet retraction and promote partial rebound, while increased AP mass concentration intensifies bubble boiling, leading to more pronounced jet ejection. The non-dimensional maximum spreading diameter (β_max) was found to decrease with rising surface temperature in deposition, partial rebound regime, and increase in explosive rebound and jet ejection regime. Additionally, the study examines the energy dissipation mechanisms during droplet impact, providing insights into the complex interactions between surface tension, viscosity, and heat transfer. The experimental maximum spreading diameter is compared with models from the literature. It was found that theoretical model modified based on the actual geometric shape and the maximum spreading time, when incorporating the dynamic contact angle at maximum spreading, have good predictive accuracy for the experimental data in this work. The evaporation behaviors revealed that higher AP mass concentrations result in earlier solute precipitation and pinning of the contact line.