Influence of spinning cup and disk atomizer configurations on droplet size and velocity characteristics

•Transition from ligament to sheet occurs in spinning cups before spinning disks.•Correlation for d32 of flat disks predicts those of the cup and disk atomizers.•Drop velocities of cup and disk atomizers are within 95% confidence of a flat disk.•The virtual slip ratio ranges between 18% and 41% for disk and cup atomizers.•Aerodynamic drag is approximately the same for disk and cup atomizers

The influence of spinning cup and disk atomizer configurations on droplet size and ejection velocity characteristics has been experimentally investigated. The Phase Doppler Particle Analyzer (PDPA) was used to measure spray characteristics in the downstream tangential distance along the spray trajectory. Four groups of both rotating disks and cups with different configurations have been experimentally studied. The first group comprises spinning disks serrated with different numbers of teeth ranging from 0 to 240. The second group includes spinning disks with different upper and lower edge angles in the range of 15° to 60°. The third set consists of spinning conical cups with different half cone angles ranging from 15° to 60° and different base diameters in the range of 0.002 to 0.06 m (2–60 mm). The last set includes spinning cylindrical cups with different heights in the range of 0.005 to 0.045 m (5–45 mm). The outer diameter of all cups and disks in all sets is 0.07 m. All experimental tests have been performed at a rotating speed of 1257 rad/s (12,000 rpm), and supply water flow rate of 2.22×10−6 m3/s (8 L/h). Measurements of Sauter mean diameter and average droplet velocity for droplets produced by studied cups and disks are compared with those of droplets produced by a regular flat disk atomizer. Comparisons indicate that all values of Sauter mean diameters and average droplet velocities for different configurations are statistically within 95% confidence level intervals around the mean of those produced by a regular flat disk. Numerically, the mean of Sauter mean diameters produced by different configurations of spinning disk and cup atomizers varied between −8% and 12% around the mean of Sauter mean diameter produced by a regular flat disk. In addition, the virtual slip ratio ranged between 18% and 41% for all atomizer configurations, while for a regular flat disk, it was 33%. The developed correlation predicting Sauter mean diameter produced by spinning regular flat disks can be satisfactorily used to predict those produced by rotating cup and disk atomizers with different configurations. In addition, the values of drag coefficient and drag force for droplets of a regular flat disk are slightly different from those calculated for investigated disk and cup atomizers.