Formation and breakup of ligaments from a rotary bell cup atomizer

Formation and breakup of ligament from a high speed rotary atomizer was investigated by using experimental observation with short flash exposure and theoretical modeling. With the aid of digital image processing, property of ligaments including trajectory, diameter and length were defined quantitatively. The droplet size distribution was measured by using particle size analyzer based on Fraunhofer diffraction theory. Conclusions are summarized as follows: (1) The liquid film is split over the grooves at the edge of a bell cup. (2) The diameter of ligament root is determined by the width of the split film in the case of lower rotational speed of bell cup, while it is determined by the instability of liquid film on the peripheral edge of cup in the case of higher rotational speed. (3) Simple kinetic model on ligament stretching motion provides good estimation on the thinning rate of ligament diameter along its axis. (4) Webers theory for the breakup model of viscous ligament well estimate the diameter of droplet of liquids having viscosity from 30 to 100 mPa·s within the uncertainty of present measurements.