Characteristics of an Electrostatically Charged Air-Atomized Spray for Pesticide Application

This paper describes a series of tests performed to evaluate the characteristics of a new system that produces electrostatically charged sprays. The system consists of a nozzle (code-named ENS) that uses air to atomize liquid pesticide into a fine spray which is simultaneously electrostatically charged and a power converter unit which supplies a 1000-V output from a 12-V battery input.

The nozzle is specifically designed for water-based pesticides applied at low flow rates on the order of 75 mL/min (1.2 gal/h). The liquid is supplied at a nominal pressure of 103 kPa (15 psig) and the atomizing air is supplied at the same nominal pressure, resulting in approximately equivalent mass flow rates for liquid and air.

The nozzle produces very fine spray quality, typically giving mean drop sizes of 15 μm both with and without the use of electrostatic charging; thus the latter can be considered an optional operating feature. Measurement of the charge/mass ratio is fundamental to understanding the behavior of electrostatically charged sprays, so considerable attention was paid to designing a satisfactory and reproducible method of making the measurement. The results showed that considerable variation in the apparent value of charge/mass ratio can occur using differing methods and at different positions relative to the spray nozzle. Consistent values on the order of 1 to 3 mC/kg were eventually obtained, however, using a Faraday cage. An endurance test of 170 h indicated no change in any characteristic.

A study was made also of the liquid flux resulting from the spray pattern produced, for both moving and non-moving targets.

Finally, a short investigation was made using four liquids having compositions typical of various pesticide carriers to determine their effect on the behavior of the ENS spray nozzle. The results were encouraging as they showed only minor differences.