Study of a droplet electrification system in a backpack sprayer in a Faraday cage

ABSTRACT This study evaluated the factors affecting the charge/mass ratio (Q/M) generated by a droplet electrification system in a backpack sprayer with an electrostatic kit, using a Faraday cage. Two experiments were conducted in completely randomized design to determine the effect of application rate, the distance between the nozzle and the target, and spraying mixtures on performance of the droplet electrification system. The first study evaluated four distances (0, 0.5, 1.0, and 2.0 m) between the nozzle and the Faraday cage; the second study was conducted in a factorial design, with five tank mixtures and five flow rates (0.25, 0.76, 1.00, 1.45, and 1.58 L min-1). The Q/M ratio was determined using a multimeter by measuring the electric current from the volume of mixture sprayed in the Faraday cage, which was divided by the respective liquid mass. Droplet spectrum was analyzed by a particle analyzer using laser diffraction. The Q/M ratio became smaller as the spraying flow rate increased, similarly as observed with increasing distances of the electrostatic nozzle from the cage entrance. The Q/M ratio increased with the addition of mineral oil, vegetable oil, and insecticide to the spraying mixture. Flow rate, distance between the nozzle and the target, and the spraying mixture affected the electrostatic spraying efficiency.

摘要
本研究借助法拉第笼（Faraday cage），针对搭载静电套件（electrostatic kit）的背负式喷雾器所采用的液滴带电系统（droplet electrification system）生成的电荷质量比（Q/M）的影响因素展开评估。本研究采用完全随机设计（completely randomized design）开展两组试验，以明确施药量、喷嘴与靶标间距以及喷雾混合液对液滴带电系统性能的影响。第一组试验设置喷嘴与法拉第笼间距四个梯度（0、0.5、1.0及2.0 m）；第二组试验采用析因设计（factorial design），涵盖5种药桶混合药液与5个流量梯度（0.25、0.76、1.00、1.45及1.58 L·min⁻¹）。电荷质量比通过万用表（multimeter）测定：先测量注入法拉第笼内的喷雾混合液的电流值，再将其除以对应药液质量即可得到该比值。采用激光衍射法（laser diffraction）借助粒子分析仪（particle analyzer）对液滴粒径谱展开分析。研究结果显示，随着喷雾流量升高，电荷质量比会随之降低；静电喷嘴（electrostatic nozzle）与法拉第笼笼口间距增大时，也会出现相同趋势。向喷雾混合液中添加矿物油（mineral oil）、植物油（vegetable oil）与杀虫剂（insecticide）后，电荷质量比会有所升高。喷雾流量、喷嘴与靶标间距以及喷雾混合液三类因素均会对静电喷雾效率（electrostatic spraying efficiency）产生影响。