Mechanisms of AIr-Assisted Liquid Atomization

A well-controlled experimental apparatus was used to investigate the air-assisted liquid drop atomization process. High-magnification, high-speed photography as well as conventional spray field photography was used to study the breakup of a monodisperse stream of drops injected into a transverse high-velocity air stream. The gas velocity profile, liquid drop velocity, and size were determined by laser Doppler velocimetry (LDV) and a phase Doppler particle analyzer (PDPA). The experiments gave information about the microscopic structure of the liquid breakup process, drop breakup regimes, drag coefficients of atomizing drops, breakup drop size distributions, and drop trajectories. At low gas-liquid relative velocities, the microscopic photographs confirmed the existence of bag and stripping breakup regimes. The photographs also revealed the nature of high-speed, "catastrophic," liquid atomization, which appears to be due to the development of instability waves on the liquid surface. A model based on aerodynamic liquid breakup theory was used to study the influences of the drop drag coefficient and the breakup time on the drop trajectory during the drop atomization process. Previously proposed expressions for the drop drag coefficient and the breakup time constant were tested by comparing the calculated trajectories with the measurements.