Meaning
Hydrodynamic fragmentation process where liquid droplets accelerated by a high-velocity gas stream undergo surface instability and split into smaller particles. A secondary Rayleigh-Taylor breakup occurs when the density difference across the droplet interface creates destabilizing pressure gradients during rapid acceleration. This mechanism is responsible for producing the fine metal powders needed for high-quality industrial applications.
Fragmentation Mechanism
Drag forces from the surrounding gas stream accelerate the droplet, creating an effective acceleration field directed from the lighter gas to the heavier liquid. Waves form on the windward side of the droplet and grow exponentially in amplitude. These waves penetrate the droplet body, causing it to deform into a thin sheet or torus before it disintegrates.
This process occurs in a fraction of a millisecond and dominates the secondary atomization stage.
Force Balance
Droplet stability during this phase is governed by the ratio of aerodynamic forces to surface tension forces. This ratio is expressed by the Weber number, with values above a certain limit indicating that the droplet will undergo fragmentation. High surface tension opposes the growth of surface waves, which stabilizes the droplet and limits further breakup.
If the metal has high viscosity, it dampens the growth rate of these instabilities and increases the required gas velocity.
Particle Resolution
Controlling the gas velocity allows operators to target specific particle sizes by manipulating this secondary disintegration. Faster gas streams generate more severe droplet acceleration, which yields a higher yield of ultra-fine powder. This adjustment is essential for producing the fine powder grades required for specialized additive manufacturing processes.
