SINOPSIS

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 D_{v 0.1}, D_{v 0.5}, and D_{v 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.