Droplet dynamics and size characterization of high-velocity airblast atomization

• Published in: International journal of multiphase flow 2017-10, Vol.95, p.1-11
• Main Authors: Urbán, András, Zaremba, Matouš, Malý, Milan, Józsa, Viktor, Jedelský, Jan
• Format: Article
• Language: English
• Subjects: Droplet size distribution; Liquid breakup; Phase-Doppler Anemometry; Plain-jet airblast atomizer; Sauter mean diameter; Spray stability
• ISSN: 0301-9322; 1879-3533
• DOI: 10.1016/j.ijmultiphaseflow.2017.02.001

•The spray from an airblast atomizer was investigated by the Phase-Doppler technique.•The drop size-velocity data determined the properties of the gas and droplet phases.•Formulae to estimate mean diameters and size distributions of sprays were evaluated.•The Gamma PDF described most accurately the size distribution of the spray. Airblast atomizers are especially useful and commonplace in liquid fuel combustion applications. However, the spray formation processes, the droplet dynamics and the final drop size distributions are still not sufficiently understood due to the coupled gas-liquid interactions and turbulence generation. Therefore, empirical and semi-empirical approaches are typically used to estimate the global spray parameters. To develop a physical understanding of the spray evolution, a plain-jet airblast atomizer was investigated in an atmospheric spray rig using the phase-Doppler technique. The simultaneous drop size and axial and radial velocity components were measured on radial traverses across the spray at various axial distances from the nozzle for a range of atomizing pressures. The droplet turbulent and mean kinetic energies were found to be proportional to the atomizing pressure. Hence, the scatter of the radial motion of the droplets increased with the atomizing pressure. A droplet stability analysis was performed to locate the regions characterized by ongoing secondary atomization. The volume-to-surface diameter, D32, of the fully developed spray was compared with estimates provided by five published formulae. The role of liquid viscosity, hence the Ohnesorge number, was found to be negligible in the investigated regime. Three commonly used size distribution functions were fitted to the measured data to analyze their dependence on the atomizing pressure. The Gamma distribution function was found to give the best approximation to the atomization process.