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Title: Characterization of air profiles impeded by plant canopies for a variable-rate air-assisted sprayer

Author
item GU, J - Nanjing Agricultural University
item Zhu, Heping
item DING, W - Nanjing Agricultural University
item WANG, X - Nanjing Agricultural University

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2014
Publication Date: 12/15/2014
Publication URL: http://handle.nal.usda.gov/10113/60584
Citation: Gu, J., Zhu, H., Ding, W., Wang, X. 2014. Characterization of air profiles impeded by plant canopies for a variable-rate air-assisted sprayer. Transactions of the ASABE. 57(5):1307-1315.

Interpretive Summary: Air jets from air assisted sprayers deflect leaves, transport spray droplets, and maintain the integrity of air velocity profile. Knowing the air jet velocity distributions will assist in choosing optimal fan parameters to minimize excessive spray drift and off-target losses from droplets passing through the canopy. Although current air-assisted sprayers provide improved spray penetration and deposition uniformity, they are not able to adjust both liquid and air flow rates as needed and thus spray losses are still considerable. Future variable-rate sprayers should have a capability to control both liquid and air flows to match tree canopy structures. This study investigated effects of the alteration of fan inlet diameter on air velocity distributions inside tree canopies of different sizes, shapes and foliage densities, and established base-line data for automatic control of air flow rates. Test results demonstrated that modifying fan inlet diameters could be an effective alternative for modifying air velocities and airflow pressures to carry droplets into plant canopies. Consequently, this study provided a viable approach in design of new pesticide sprayers to achieve efficient variable air flow rates for precision pesticide applications.

Technical Abstract: The preferential design for variable-rate orchard and nursery sprayers relies on tree structure to control liquid and air flow rates. Demand for this advanced feature has been incremental as the public demand on reduction of 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 variable air rate capability by changing the fan inlet diameter of the sprayer, air jet velocities impeded by plant canopies were measured at various locations inside canopies of three different tree sizes and foliage densities. Air jet velocities were adjusted by changing the sprayer fan inlet diameters 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, airflow pressure ratio of front portion to back portion of the canopies was 2.45 for a 1.65 m tall and 13.4 leaf area index (LAI) Tsuga canadensis, 1.43 for a 2.35 m tall and 2.5 LAI Ficus benjamina, and 1.64 for a 3.0 m tall and 1.5 LAI Acer rubrum. Similarly, the front to back peak air velocity ratio was 8.55, 1.59, and 1.89 times for T. canadensis, F. benjamina and A. rubrum, 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, 3.88 to 5.82 kg m-2, and 2.46 to 3.75 kg m-2 inside canopies of T. canadensis, F. benjamina and A. rubrum, respectively, while it also increased average peak air velocity from 2.6 to 4.5 m s-1, 5.5 to 9.1 m s-1, and 3.0 to 5.2 m s-1 inside these three tree canopies. Therefore, the new sprayer design with the airflow regulator to alter the fan inlet diameter was able to provide variable air flows 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 for efficient pesticide applications.