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Doctoral thesis, 2001

Converging air jets in orchard spraying : influence on deposition, air velocities and forces on trees

Svensson, Sven Axel


To provide necessary plant protection in orchards, spray drops are transported to and into the apple tree canopy with an air jet from a fan sprayer. The interaction between the spray air jet and the canopy is central to effective droplet transport, spray coverage and pest control. Converging air jets were introduced as a way of improving the spray application. In this study, a two unit cross-flow fan orchard sprayer, configured as converging or plane (vertical fan units) air jets, were compared in several experiments. Inclining the top or bottom fans towards the tree created different types of 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 throughout the season with fluorescent tracer on leaf sized filterpaper targets inside canopies. Different types of air velocity measurements were made with the fan sprayer passing the tree. Peak velocities were recorded at positions throughout apple tree canopies, and indepth measurements of several air velocity parameters were made inside, above and beyond an apple tree canopy. Velocity pulse values were integrated over time. Air velocity profiles were measured in stationary situations and compared to existing mathematical models. Forces and moments caused by the air jet striking the tree were measured with a new method, utilizing a multicomponent 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. This could be explained by the ability of the converging air jets to reduce the air flow directed above the trees, thereby concentrate and increase the 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. Keywords: air jets, air velocity measurements, anemometer, apple, application technology, canopy, converging air jet, cross-flow fan, fan sprayer, fluorescent tracer, force measurements, force transducer, orchard spraying, pest control, plant protection. Author’s address: Sven Axel Svensson, Department of Agricultural Engineering, SLU, Box 66, SE-230 53 ALNARP, Sweden.


air jets; air velocity measurements; anemometer; apple; application technology; canopy; converging air jet; cross-flow fan; orchard spraying; pest control; plant protection

Published in

Acta Universitatis Agriculturae Sueciae. Agraria
2001, number: 279
ISBN: 91-576-5818-8
Publisher: Swedish University of Agricultural Sciences

Authors' information

Svensson, Sven Axel
Swedish University of Agricultural Sciences, Department of Agricultural Engineering

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