Measurement of Single Droplet Characteristics using High Speed Imaging Techniques

Abstract : The spray droplets generated by agricultural nozzles play an important role in the application accuracy and efficiency of plant protection products. But, the process of generating and controlling small droplets of high uniformity, constant size and form is complex and difficult to quantify or model. 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 in pesticide spray characterisation. The goal of this study was to apply an imaging technique to evaluate the characteristics of a single spray droplet using a piezoelectric single droplet generator in a droplet-on-demand mode with 4 glass nozzles and a high speed imaging technique. Tests were done with a high-speed camera, microscope lenses, and a xenon light source. Image analysis algorithms were developed for droplet sizing and tracking on images gained from this acquisition system. The experiments have shown that using the selected image acquisition and processing system, different droplet sizes and velocities can be measured. By changing the pulse width and the nozzle orifice size, repeatable droplets could be generated with a size ranging from 135 μm up to 461 μm. The ratio between droplet diameter and nozzles orifice opening varied from 1.33 up to 3.42 depending on the settings.