High-speed Imaging Of Molten Droplet Atomization Inside And Outside A Supersonic Gas Jet

To elucidate the gas atomization process as a thermo-fluid phenomenon, we successfully performed high-speed Schlieren imaging up to one million frame per second for the first time to resolve deformation and fragmentation of a tin droplet subjected to a supersonic nitrogen jet at Mach number of 1.5. We identify two atomization processes by tracking the deforming ligaments in a Lagrangian manner. Inside the supersonic jet, the large aerodynamic force shears the droplet into tiny particles partially interacting with the shock waves inside the jet. Rebounded above the jet, the rest droplet deforms to be ligaments, which break dominated by the capillarity producing large particles. We find that the distinct atomization mechanisms result in a bi-modal distribution of the produced particle size. This fact indicates that the molten droplets in a practical apparatus collide with gas jets at multiple times, leading to a converged mono-modal distribution.