Evaluation of the spray characteristics of a single droplet with imaging techniques

The spray droplet generated by agricultural nozzles plays an important role in the application accuracy and efficiency of plant protection products. Nevertheless, the mechanisms of droplets leaving a spray nozzle and impacting the leaves are very complex, difficult to quantify or model and the existing techniques are not able to fully characterize the spray application process; therefore a need for accurate quantification techniques exists. The limitations of the non-imaging techniques and the recent improvements in digital image acquisition and processing increased the interest in using high speed imaging techniques for pesticide spray characterisation.
The goal of this study is to evaluate the characteristics of a spray droplet using a piezoelectric single droplet generator and a high speed imaging technique.
The build image acquisition set-up for measuring droplet size and velocity consists of a high speed camera (N3, IDT), a microscope lens (K2/SC Long-Distance Microscope Lens, Infinity) at 6 µs exposure time selected from a frame software (Motion Studio, IDT) installed on a computer and a Xenon light (WOLF 5132) used as a backlight.
The experiments with a droplet generator are done in DOD (drop-on-demand) mode. Moreover, by changing the characteristics of the input signal in NI LabVIEW, we are able to create different droplet sizes similar to those obtained with sprayers. The images from different glass nozzles of sizes (50 µm – 200 µm) are taken at 1000 fps and analyzed in Matlab using image processing algorithms. As a result, we are able to determine the droplet size and velocity from different nozzles.
To conclude, a measuring set-up and imaging technique are developed to generate single spray droplets and measure their characteristics. The experiments have shown that the initial characteristics of the droplet are a function of the pulse width and the voltage amplitude.