Effects of electrostatically charging pesticide sprays and quantitative methods for measuring spray efficacy. (2020)
Type of ContentTheses / Dissertations
Thesis DisciplineMechanical Engineering
Degree NameMaster of Engineering
PublisherUniversity of Canterbury
AuthorsLongworth, Lukeshow all
Traditional pesticide spraying procedures are often wasteful, with large proportions of the spray missing the target plants and drifting to unwanted locations. Electrostatically charging the spray can enhance the process, reducing loss and improving coverage on hidden surfaces. This thesis describes an investigation into the various parameters that can increase the effectiveness of an electrostatic nozzle, and how these and geometric parameters can increase the efficacy of spray. Additionally, an investigation into the use of capacitive wetness sensors to test spray efficacy was performed.
Increasing liquid flow rate through the nozzle was a major contributor to increasing nozzle charge-to-mass ratio, with increasing electrode voltage playing a more minor, but still noticeable role. The sensor specifications of the PHYTOS 31 capacitive wetness sensors were measured and recorded, and two calibration functions that convert sensor output to areal coverage were produced; one for large droplets (>1 mm) and the other for fine sprays (<1 mm). These sensors were also compared to water sensitive papers and found to be a suitable substitute for spray coverage measurements, though it should be noted that whilst papers measure the integral of coverage over time, the capacitive sensors measure instantaneous coverage. Finally, it was found that the wrap-around effect of electrostatic sprays is most effective on surfaces facing 0° – 60° away from the spray axis, and on surfaces 8° below the spray axis. Additionally, canopy penetration was improved by charging the spray, though this effect does not persist at the back of the canopy. Canopy penetration is found to improve as voltage increases, though there is a peak voltage of around 3.5 kV beyond which there is no clear evidence of further improvement.