Submitted to: Aspects of Applied Biology
Publication Type: Proceedings
Publication Acceptance Date: 11/19/2001
Publication Date: N/A
Citation: Interpretive Summary: Air-assisted sprayers use air-jets to transport spray droplets into the plant canopy and promote uniform deposition of the spray throughout the canopy. Air-jet velocity and volume, jet exit direction with respect to the sprayed tree, size and growth stage of the tree, volume, distribution and drop size of spray solution applied, as well as wind conditions all may affect the deposition pattern of the spray. We used hot-film sensors to measure air velocities at several locations within and near apple tree canopies and developed a new method for measuring the force applied to the tree in the cross-row direction and the moment about the tree row axis. A two unit, cross-flow fan sprayer was driven past trees and velocities within the tree or forces on the tree due to the sprayer air-jet were measured. Plane jets (both fans vertical) and converging jets (top fan inclined 19 deg. toward the tree) were used. There was greater variation among air velocities, measured at a point, than among forces, which averaged jet/tree interactions over the entire tree. The converging jet produced greater air velocities in the densest part of the tree canopy and also produced the greatest forces and moments on trees. Because tree foliage is moved by the sprayer air-jet, it is difficult to obtain statistically significant differences among spray deposit measurements or among air velocities measured within a tree canopy. The force method produced significant differences among treatments. These methods are shown to be useful tools in orchard spraying research and will likely be adopted by researchers around the world and by manufacturers for testing the effectiveness of orchard sprayers.
Technical Abstract: In this study, a two unit cross-flow fan orchard sprayer, configured as converging or plane (vertical) air jets, were compared in several experiments. Inclining the top or bottom fans towards the tree created converging air jets. The influence of these air jets on spray deposition, on air velocities and on forces acting on apple trees was measured. Deposition was measured with fluorescent tracer on leaf sized filter paper targets inside canopies. Air velocity measurements were made with the fan sprayer passing the tree. Peak velocities were recorded at positions throughout apple tree canopies and in-depth measurements of several air velocity parameters were made inside, above and beyond an apple tree canopy. Velocity pulse values were integrated over time. Forces and moments caused by the air jet striking the tree were measured with a new method, utilizing a multi-component force transducer, placed between the tree trunk and the ground. Compared to plane air jets, converging air jets resulted in significantly higher deposition values, more uniformly distributed through the canopy. The converging air jets increased the air velocity parameters in the denser parts of the canopy and resulted in higher air power and energy at those positions. Converging air jets transferred greater forces to the canopy. Converging air jets reduced air flow directed above the trees, thereby concentrated and increased amount of spray liquid penetrating into the densest part of the canopy. Finally, an increased air velocity improved deposition prerequisites. The new method for measuring forces and moments has a potential to extend and complement other application technology measuring methods.