Atmospheric drift of plant protection products is considered a major source of air pollution during pesticide applications. Citrus protection against pests and diseases usually requires application of these products using air-blast sprayers. Many authors have emphasized the influence of vegetation on the risk of spray drift. The aim of this work was to describe in detail how the airflow from an air-blast sprayer behaves when it reaches citrus trees and, in particular, the effect that the tree canopy has on this flow. Tests were conducted at a commercial citrus orchard with conventional machinery, placed parallel to a row of trees. Air velocity and direction was measured using a 3D ultrasonic anemometer in 225 points situated in three parallel planes perpendicular to the equipment. The stability of the airflow at each measuring point was studied and the mean velocities were graphically represented. Two vortexes, one behind the canopy, and another over the tree, have been deducted and never been reported before. Both may have an important influence on the trajectories of the sprayed droplets and, as a consequence, on the way in which plant protection products are diffused into the atmosphere. Observed turbulence intensities were higher than in similar experiments conducted in other tree crops, which may be attributable to the higher air volume generated by the machinery used for citrus protection and to the higher foliage density of citrus orchards.
ElsevierSalcedo Cidoncha, R.; Granell Ruiz, R.; Palau-Salvador, G.; Vallet, A.; Garcerá, C.; Chueca, P.; Moltó, E. (2015). Design proposes and validates a two dimensional CFD model to be applied in citrus tree 19
During pesticide applications to citrus trees using air-assisted (airblast) sprayers, only a proportion of the volume emitted reaches the vegetation and the rest is lost through drift, evaporation, etc. These losses can be hazardous for the environment. Knowing the characteristics of droplets within the turbulent currents around the canopy could improve the application efficiency. In a previous study, a 2D computational fluid dynamics (CFD) model was used to simulate the effect of a citrus canopy on the airflow from an airassisted sprayer was developed and validated. It considered the first element of the tree canopy as a solid body instead of a porous one. The aim of this study was to analyse the behaviour of the droplets for pesticide applications on citrus by means of an Eulerian-Lagrangian CFD model. It simulated both the air current from the sprayer fan and the wind and the behaviour of the droplets sprayed. Distance, height, velocity, Reynolds number, temperature, geometric and volumetric diameters at different times were obtained. With these parameters, new variables related to the kinetics and evaporation droplets were calculated. Simulation results estimated that 44% of the total sprayed volume reached the target tree, 28% reached adjacent trees, 20% was deposited on the ground and 8% was lost as atmospheric drift. The results largely matched an experimental mass balance carried out under similar conditions. The proposed model appears to be an appropriate tool for simulating treatments with air-assisted sprayers operating in citrus orchards.
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