Reducing Driftable Fines in Aerial Application of Pesticides by Controlling Nozzle Environment

Spray drift is one of the most significant issues facing aerial applicators. Material not applied to the target crop or pest is a financial loss for the farmer and a potential liability for the applicator. Off-site drift also represents an environmental liability, particularly as habitat and water quality concerns demand greater attention with larger buffer and/or no-spray zones. Current practice delivers liquid material through a nozzle, under pressure, and utilizes air shear for at least a portion of the atomization, creating a range of droplets with those less than 200 microns, known as fines, particularly susceptible to off-site drift. As airspeed increases, so does the effect of air shear on the spray leaving the nozzle, resulting in further shatter/fracture of droplets producing even more fines, leading to more off-site drift. Control of the nozzle environment allows for control of air velocity where atomization occurs, reducing the production of driftable fines and reducing off-site movement of spray material. Control of nozzle environment is accomplished using a chamber having three sections, called a Reverse Venturi Atomization Chamber (RVA). Air enters the first section (diffuser), with a restricted opening, and flows into a larger area (settling chamber) where air velocities are reduced, the nozzle is located, and where atomization occurs. The atomized spray and air then travel through the third chamber section (constrictor) where they are accelerated to match the aircraft’s air speed. By reducing the air speed were atomization occurs, the atomization profile demonstrates fewer fines, leading to less drift. Data to date, using the prototype RVA, water as the test medium, and a selection of commercially available nozzles, we have demonstrated up to a 74 % reduction in fines at 100 mph and 58 % reduction in fines at 150 mph air speed