Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2011
Publication Date: 12/30/2011
Citation: Huang, Y., Thomson, S.J. 2011. Characterization of in-swath spray deposition for CP-11TT flat-fan nozzles used in low volume aerial application of crop production and protection materials. Transactions of the ASABE. 54(6):1973-1979.
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 result in the number of driftable fines (those droplets under approximately 100 µm diameter). Tests were conducted at three low volume flowrates to determine droplet parameters for the CP 11-TT flat fan nozzle. Seven spray cards were placed in the swath for each run to evaluate median droplet size, droplet size range, and % coverage on the cards as a function of application height, nozzle angle, and flowrate. Weather variables were also measured so that their influence could be determined statistically. The USDA Droplet Spectrum 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 from this study were compared with model results, and 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, indicating less drift potential.
Technical Abstract: For aerial application of crop production and protection materials, a complex interaction of controllable and uncontrollable factors is involved. It is difficult to completely characterize spray drift and deposition, but estimates can be made with appropriate sampling protocol and analysis. With careful consideration of these variables that includes accurate measurement of application altitude, improved characterization is possible. This study was designed to investigate the low drift CP flat-fan nozzle for characterization of in-swath spray deposition. In the study, CP flat-fan nozzles with selectable tips and swivel angles were evaluated for droplet spectra and coverage using water sensitive papers placed in the spray swath. Low application volumes (9.5, 19, and 28.5 L/ha) were used at 3.66 m spray application height as measured precisely by a laser mounted in the aircraft. Nozzle angles were adjusted with the CP swivel, and appropriate flat-fan tips were specified according to the desired 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. Statistical results showed the trend of higher spray flow rates resulting in higher percentage spray coverage. Among weather variables, relative humidity had a significant effect on spray coverage (p=0.0007). Average Dv0.5 did not differ much between the 30 and 45 degree downward angles, but average Dv0.5 for the 15 degree angle was 50% higher than that for the 30 and 45 degree angles. Field results compared favorably with output of the USDA Droplet Spectrum Models at all flowrates. Relative span, which is an indication of droplet size ranges, was slightly lower in field trials than those indicated by the USDA models. 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.