in Wiley Online Library (wileyonlinelibrary.com).The influence of impact conditions (reported in terms of Weber and Reynolds numbers) on nucleus formation was studied for single drops striking a static glass bead bed. Results from high speed images showed that the nucleation rate is not influenced by liquid physical properties (density, surface tension, viscosity) for drops that spread significantly (30 \ We \ 233). Results also showed that nucleus size is determined by how much liquid penetrates into the bed during drop spreading, so does depend on surface tension and liquid density. A corresponding analytical model, derived from first principles, predicts nucleus size to with 1.5% using only liquid physical and powder bed properties, plus the experimentally measured drop spreading behavior.

An experimental study was conducted to characterize the performance of a hybrid atomizer used in emission control devices. Characterization included drop size distribution, measured using a forward light-scattering instrument, the air flow field (axial and radial velocities), measured using 2-D PIV, and turbulence characteristics of the air flow field, measured using LDA. The air flow field showed characteristics common to turbulent free round jets beyond approximately 8 exit orifice diameters from the atomizer exit plane. The centerline velocity increased with an increase in mass flow rate, while radial velocities were two orders of magnitude smaller than centerline values. The jet spreading factor initially increased with an increase in axial distance from the exit; however, it stabilized at a value of 0.09 at z/Do=11.8. Turbulence intensity along the jet centerline stabilized at 25% at z/Do=7.9. Drop size data showed complex dependencies on liquid and air mass flow rates, and on internal geometry. The influence of liquid mass flow rate on drop size was significantly smaller for the hybrid atomizer than for the pressure swirl atomizer component housed inside the hybrid unit, thus indicating a higher turndown ratio for the hybrid device. Drop size distributions produced by the hybrid atomizer showed multiple peaks, indicating there is more than one important atomizing mechanism. Finally, reducing the gap between the pressure-swirl atomizer and the exit plane of the outer casing resulted in a reduction in drop size.