Spatial droplet velocity and size profiles in effervescent atomizer-produced sprays

Abstract

Effervescent atomizer produced sprays were studied for application to rotary kiln incinerators. The sprays were characterized by their number averaged droplet velocity profiles, Sauter mean diameter (SMD) profiles, and size-velocity correlations. Spray mass flow rates ranged from 30 to 120 g/s. Air-liquid-ratios by mass (ALRs) were between 2% and 10%. Data were obtained at seven to ten radial positions across the diameter of the spray at three separate axial locations, all in the far-field (or dilute region) of the spray. The number averaged droplet velocity profiles were bell-shaped across any diameter, irrespective of ALR, liquid mass flow rate, or axial location. Velocity magnitudes were found to increase with an increase in either liquid mass flow rate or ALR, and to decrease with an increase in axial distance from the atomizer exit. SMD was found to be nearly constant across any spray diameter. On the basis of velocity-size-number flux contour plots, it was determined that the droplet size-velocity correlation is minimal. This observation, coupled with the minimal variation in SMD across a diameter, indicates that the spray can be modeled as a variable-density single-phase jet. A model was developed, based on previous gas-phase studies, to explain the development of the drop velocity profiles in the dilute spray region. Agreement between the measured drop velocities and model predictions was within 30% in all cases.