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

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 and 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 charge-to-mass ratio (Q/M > 1.0 mC kg-1) compared to the TXVK-4 and TXVK-6 nozzles. At 310 kPa liquid pressure, 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.