Gap optimization of electrostatic aerial spray nozzles for low-speed aircraft

Authors: Martin, Daniel - Dan; Latheef, Mohamed - Ab; Duke, Sara

Submitted to: Journal of Electrostatics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2022
Publication Date: 4/18/2022
Citation: Martin, D.E., Latheef, M.A., Duke, S.E. 2022. Gap optimization of electrostatic aerial spray nozzles for low-speed aircraft. Journal of Electrostatics. https://doi.org/10.1016/j.elstat.2022.103714.
DOI: https://doi.org/10.1016/j.elstat.2022.103714

Interpretive Summary: Aerial electrostatic spray nozzles induce a charge on spray droplets as they exit the nozzle. This charge helps increase deposition of these droplets onto pest targets, whether they be insect pests, weeds or plants with disease. Wind tunnel studies were conducted to determine the effects of electrode gap, nozzle orifice, airspeed and pressure on spray chargeability from a commercial aerial electrostatic spray nozzle. The work established that the smaller orifice nozzle at the lowest spray pressure and the highest airspeed produced the greatest charge of the spray plume. Each nozzle tip had a very specific gap that provided the best spray chargeability for the different operational parameters. Commercial pesticide applicators and researchers will be able to use this information to increase spray deposition and efficacy of aerial applications while reducing off-target spray drift.

Technical Abstract: The gap between the spray plume and the cylindrical charging electrode for an aerial electrostatic spray nozzle is critical to achieve maximum chargeability of spray formulations prior to aerial applications of pest control products. Seven discrete gaps from the nozzle tip to the trailing edge of the electrode were tested for spray chargeability. A spray mixture of tap water and a non-ionic surfactant with an electrical conductivity of 1012.75 ± 6.70 µS was atomized through three different-sized nozzle tips (TXVK-3, TXVK-4, and TXVK-6) in a controlled high-speed wind tunnel operated at 6 different airspeeds between 80 to 177 km/h with two atomizing air pressures, 310 and 517 kPa, representing minimum and maximum values commonly used in rotary wing agricultural aircraft. The TXVK-3 nozzle yielded significantly higher spray charge-to-mass ratio (Q/M >1.0 mC kg-1) compared to the TXVK-4 and TXVK-6 nozzles. Similarly, the 6.5 and 9.3 mm gaps produced significantly higher spray charge. Data indicated that the chargeability of aerial electrostatic sprays can be improved using a smaller orifice and lower flow rate nozzle operated at a lower liquid pressure and higher airspeed. Results from this study may help aerial applicators better understand the optimum operational parameters required to maximize the electrostatic charge of spray formulations while flying low speed aircraft.