Characterization of Air Profiles Impeded by Plant Canopies for a Variable-Rate Air-Assisted Sprayer
Abstract. The preferential design for variable-rate orchard and nursery sprayers requires that the sprayers are able to control the liquid and air flow rates based on the canopy structure in real time. Demand for this advanced feature has increased rapidly with the public demand for reductions in pesticide use. A variable-rate, air-assisted, five-port sprayer had been in development to achieve variable discharge rates of both liquid and air. To verify the capability of varying the airflow rate by changing the fan inlet diameter of the sprayer, air jet velocities impeded by plant canopies were measured at various locations inside tree canopies of three different sizes and foliage densities. Air jet velocities were adjusted by changing the sprayer fan inlet diameter with an airflow regulator and measured with a constant-temperature anemometer coupled with hot-wire probes. Peak air velocity and airflow pressure decreased with foliage density and canopy depth. For the 0.34 m fan inlet diameter, the airflow pressure ratio of the front portion to the back portion of the canopies was 2.45 for a 1.65 m tall and 13.4 leaf area index (LAI) Tsuga canadensis (Tree 1), 1.43 for a 2.35 m tall and 2.5 LAI Ficus benjamina (Tree 2), and 1.64 for a 3.0 m tall and 1.5 LAI Acer rubrum (Tree 3). Similarly, the front-to-back peak air velocity ratios were 8.55, 1.59, and 1.89 for Tree 1, Tree 2, and Tree 3, respectively. Variations were significant for peak air velocities and airflow pressures among the three different tree volumes and foliage densities. Increasing the fan inlet diameter from 0.13 to 0.34 m increased average airflow pressure from 2.84 to 4.01 kg m -2 , from 3.88 to 5.82 kg m -2 , and from 2.46 to 3.75 kg m -2 inside the canopies of Tree 1, Tree 2, and Tree 3, respectively, while it also increased average peak air velocity from 2.6 to 4.5 m s -1 , from 5.5 to 9.1 m s -1 , and from 3.0 to 5.2 m s -1 inside the three tree canopies. Therefore, the new sprayer design with an airflow regulator to alter the fan inlet diameter was able to provide variable airflow for different canopy sizes and foliage densities and offered a potentially effective approach to discharge uniform airflow profiles to carry droplets with efficient spray penetration into plant canopies.