DROPLET SIZE DISTRIBUTIONS OF ADJUVANT-AMENDED SPRAYS FROM AN AIR-ASSISTED FIVE-PORT PWM NOZZLE

Verification of droplet size distributions is essential for the development of real-time variable-rate sprayers that synchronize spray outputs with canopy structures. Droplet sizes from a custom-designed, air-assisted, five-port nozzle coupled with a pulse-width-modulated (PWM) solenoid valve were measured under various operating conditions. Parameters included five air velocities (0, 10, 30, 50, 70 m/s), three spray solutions (water-only, a water-surfactant solution, and a water-drift-retardant solution), five operating pressures (138, 207, 276, 345, 414 kPa), and seven pulse-width-modulation rates (10, 20, 40, 50, 60, 80, 100%). Droplet sizes did not vary significantly with modulation rates of 20-100%. The variation of droplet size was highly significant with spray solution formulation and operation pressure and was slightly significant with air velocity. A dimensionless parameter, which was the ratio of liquid viscosity and relative discharge velocity to surface tension, was correlated with Dv 0.1, Dv 0.5, and Dv 0.9 of droplets for the three spray solutions. Droplet size variations were minimized when the variable-rate nozzle was operated at a constant liquid pressure and when a 10% or lower modulation rate was not used. The variation of droplet sizes due to changes in the air velocity for water-only and surfactant-amended sprays was acceptable for the new sprayer development.