Patternator Testing - 2012
Droplet Density
Droplet density is measured in droplets per square centimeter. With an air blast sprayer, a high velocity stream of air initially carries the spray droplets horizontal to the ground. Droplets can be sheared apart and combined by the stream of air. The high velocity air also initially moves droplets across the card surface before they are absorbed on the card creating many oval and elongated shapes. Many of the droplets overlap with other droplets creating odd non-circular shapes. All of these variables create a situation where it is difficult to determine droplet density with both the NESareScan and DepositScan programs using an air blast sprayer.
No correlation could be found between droplet density and percent coverage with either program. Droplet density varied substantially between cards with nearly the same percent coverage in both programs. Neither the NESareScan program or the DepositScan program should be utilized when trying to determine droplet density with an air blast sprayer. The volume of spray and the dynamics of an airblast sprayer create a spray pattern that is nearly impossible to read in regards to the droplet density.
The programs might work better with a boom sprayer. No testing was done with a boom sprayer. When using a boom sprayer, spray droplets fall downward from gravity and the pressure of the sprayer system. The amount of spray coverage on a surface with a boom sprayer is usually much less than that encountered when using an air blast sprayer. The integrity of the spray droplets is much more consistent with a boom sprayer.