Air velocity distributions inside tree canopies from a variable-rate air-assisted sprayer

Abstract

Abstract. 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. Tree heights were 1.65, 2.35 and 3.0 m, and leaf area indexes were 13.4, 2.5, and 1.5, respectively. Air jet velocities were adjusted by changing the sprayer fan inlet diameters and measured with a constant temperature anemometer coupled with hot-wire sensors. Peak air velocity and airflow pressure decreased as the foliage density and canopy depth increased. For the 0.34 m fan inlet diameter, airflow pressure ratio of front portion to back portion of the canopies was 2.45, 1.43 and 1.64 for Tsuga canadensis, Ficus benjamina and Acer rubrum, respectively. 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. Increased fan inlet diameters from 0.13 to 0.34 m, increased average airflow pressure from 2.84 to 4.01, 3.88 to 5.82 kg/m2, and 2.46 to 3.75 kg/m2 inside canopies of T. canadensis, F. benjamina and A. rubrum , respectively. Therefore, alterations of fan inlet diameters for the five-port air assisted sprayer achieved variable air flow rates for different canopy sizes and foliage densities.