Atomization and Sprays, Vol.21, No.12, 1009-1031, 2011
STEADY AND TRANSIENT DROPLET DISPERSION IN AN AIR-ASSIST INTERNALLY MIXING CONE ATOMIZER
Droplet dispersion for steady and transient sprays produced by an air-assist internally mixing cone atomizer is studied using high-speed laser imaging, shadowgraphy, and particle tracking velocimetry (PTV). For this spray, large droplets form close to the periphery while small droplets form close to the centerline. Radial dispersion of droplets is a function of droplet relaxation time and fluctuating flow characteristic times so that small droplets disperse more effectively in the radial direction than large droplets due to turbulent diffusion. For the transient spray, the overall axial and radial penetration of the spray is self-preserving and similar to penetration of starting continuous phase jets. Axial dispersion of droplets is a function of droplet relaxation time and the mean flow characteristic time. The leading edge of the spray exhibits higher turbulence than the trailing edge, which is characterized by very large eddies and smaller Reynolds numbers. The dispersion behavior at far-field away from the breakup region is expected to be similar for many dilute air-assist, internally mixing round sprays.
Keywords:air-assist;internally mixing;spray;atomizer;droplet;dispersion;starting jet;imaging;shadowgraphy;particle tracking velocimetry (PTV)