ARS | Publication request: In-Swath Spray Deposition Characteristics of a Low Drift Nozzle for Low Volume Aerial Application

Submitted to: National Agricultural Aviation Association Meeting
Publication Type: Proceedings
Publication Acceptance Date: December 8, 2008
Publication Date: December 8, 2008
Citation: Huang, Y., Thomson, S.J. 2008. In-Swath Spray Deposition Characteristics of a Low Drift Nozzle for Low Volume Aerial Application - Preliminary Results. ASABE Technical Session in 42nd Annual National Agricultural Aviation Association Convention. December 8-11, 2008, Las Vegas, Nevada. ASABE paper number: AA08-003

Interpretive Summary: When using nozzles on agricultural aircraft for application of material, proper nozzle selection and setup are important. Low drift nozzles have been designed to promote a narrow range of droplet sizes, which is important for reduction of off-target drift. A narrow spectrum may reduce the number of driftable fines (those droplets under approximately 100 µm diameter) for a given median droplet diameter. Application height can influence the potential for off-target drift, and this is frequently not considered carefully enough in spray evaluations. Tests were conducted at three low volume flowrates to determine droplet spectra and deposition for the CP 11-TT flat fan nozzle. Seven spray cards were placed in the swath for each run to both evaluate median droplet size, droplet size range, and % coverage on the cards as a function of nozzle angle and flowrate. Application height varied within 15 feet, and this was measured accurately by an on-board laser. Weather variables were also measured so that their influence could be determined statistically. Nozzle angle and Relative Humidity (RH) had a significant influence on the amount of spray coverage on cards. Interestingly, spray altitude did not have a significant effect on coverage for these particular nozzles, but preliminary data suggested an influence on droplet spectrum. Results from this study were compared with results using the USDA Droplet Spectrum Models. These models are designed to assist in selecting the proper nozzle, and they output droplet spectrum values as a function of nozzle type, operating pressure, speed of the aircraft, nozzle angle and other parameters. Results showed that Volume Median Diameter, VMD (or DV 0.5) - the droplet diameter (µm) where 50% of the spray volume or mass is contained in droplets smaller than this value - was the best fit of all parameters. Droplet size ranges were actually narrower than the models predicted for most runs, which is indicative of less drift potential when using these nozzles.

Technical Abstract: CP flat-fan nozzles with selectable tips were evaluated for droplet spectra and coverage using water sensitive papers placed in the spray swath. This study used low application volumes (1, 2, and 3 GPA) at a certain spray application height as measured precisely by laser mounted in the aircraft. Nozzle angles and flowrates were adjusted for the nozzles, and appropriate tips were specified according to required flowrate. With the interaction of these application variables, droplet spectra of the water sensitive papers over the spray swath were calculated to produce Dv0.1, Dv0.5, Dv0.9, and relative span. The effects of application flowrate, nozzle angle, and weather variables on the droplet spectrum and coverage were determined statistically. Processed data were compared with output from the available USDA Droplet Spectrum Models at the three low volumes, and spray patterns in the swath were indicated graphically. Baseline data obtained in the swath on droplet characteristics can help aerial applicators verify the correct spray tip for a given flowrate and nozzle angle for a desired droplet spectrum and sufficient spray coverage.