Meaning
Longitudinal and transverse disturbances in a liquid stream cause the coherent core to break into smaller fragments. Studying dynamic wave instability provides the theoretical basis for predicting how quickly a molten metal jet will transition into a spray of fine droplets. This breakdown is driven by the interaction of inertia, surface tension and gas phase shear forces acting upon the interface.
Growth Phase
Small perturbations on the surface of the metal expand rapidly when exposed to high velocity gas flows. As dynamic wave instability increases, the liquid column develops visible ridges that eventually shear off into ligaments. The rate of this expansion determines the starting size of the primary droplets before secondary fragmentation begins.
Frequency Modulation
Variations in the gas inlet pressure can shift the dominant frequency of the vibrations seen in the melt stream. When dynamic wave instability occurs at high frequencies, the result is typically a finer powder with a more uniform size range. Lower frequency oscillations tend to produce larger irregular pieces that require more energy to further refine.
Breakup Timing
Duration between initial gas contact and complete liquid dispersion depends on the speed of wave growth. Managing dynamic wave instability involves tuning the gas flow to maximize the shearing effect while minimizing erratic bursts. Stable waves lead to a steady state process that is easier to monitor with visual equipment.
