Measurements of reference ISO nozzles by high-speed imaging. (November 2016)

• Record Type: Journal Article
• Authors: De Cock, Nicolas; Massinon, Mathieu; Nuyttens, David; Dekeyser, Donald; Lebeau, Frédéric
• Is Part Of: Crop protection. Volume 89(2016)
• Page Start: 105
• Page End: 115
• Publication Date: 2016-11
• Subjects: Droplet sizing -- Digital image analysis -- Agricultural spray -- ISO/DIS 25358; Plants, Protection of -- Periodicals; 632.05
• DOI: 10.1016/j.cropro.2016.07.016
• Languages: English
• ISSNs: 0261-2194

Abstract

Abstract: Agricultural spray characteristics determine the efficiency of a pesticide application because size and velocity affect droplet trajectory and impact behavior. At present, the relevance of different characterization techniques remains controversial since discrepancies may be significant between measurements performed in different laboratories. A digital image acquisition technique and analysis algorithm is proposed for droplet size and velocimetry measurements as an alternative to well-established techniques such as the Phase Doppler Particle Analyzer (PDPA) or laser diffraction spectrometry (LDS). The algorithm requires double exposed shadow images acquired in a back-lighted arrangement with a Particle Image Velocimetry (PIV) camera and a pulsed light emitting diode (LED). Spatial illumination heterogeneities are corrected by subtracting from each image a mean background acquired on several images without any particle. The algorithm accuracy is ensured by the rejection of out-of-focus particles using a focus parameter depending on gradient intensity at the particle edges. Thresholds for focus particle selection were determined by studying the evolution of the focus parameter and the error on particle size measurements from images containing droplets with uniform size at various distance of the object plane. Selected droplets were identified on both pairs of images to determine their size and velocity. Droplet size distributions were corrected to account for the uneven sampling probability caused by the volumetric method. Droplet size distributions of a set of reference nozzle/pressure combinations defined in the ISO/DIS 25358 were measured. The image technique was able to distinguish each of the reference sprays well. Comparison with PDPA measurements showed that the imaging technique tends to measure an equivalent Dv 50, a lower Dv 10 and a higher Dv 90 leading therefore to a higher relative span factor. Velocity measurements showed good agreement between both techniques except for one nozzle/pressure combination. Highlights: An image processing algorithm for droplet size and speed measurements is proposed. Droplet size distributions of reference nozzle-pressure combinations were measured. The 6 sprays droplet size distributions were well differentiated by the imaging. Comparative measurements with Phase Doppler Particle Analyzer have been done. Coarser sprays measurements show significative differences between the two techniques.