Nozzle wear effect on droplet size characteristics: VMD, V100, relative span factor, and velocity

Spray droplet size spectra of nozzles play a key role in effective spray applications, as they directly affect spray distribution quality. However, continuous chemical spraying can cause nozzle wear, leading to physical alterations of the nozzle orifice and, consequently, changes in spray volume and droplet size. Although evaluating the effect of the nozzle wear on spray quality was the primary work in this research, the effect on droplet velocity and relative span factor (RSF) was also investigated due to their significancy in spray application efficacy and drift potentials. Evaluations included measurements of droplet size spectrum, droplet velocity, and RSF of three ISO 110 02 conventional flat fan nozzles with three different tip materials: i) ceramic, ii) polymer, and iii) stainless-steel. These nozzles underwent accelerated wear tests with the ISO standard 5682-1:2017 to simulate nozzle wear. Nozzle-wearing degree was examined by measuring the flow rate at defined time intervals after the new tips were used. Before and after each test, volumetric droplet sizes (Dv0.1, Dv0.5, and Dv0.9), V100 (percent total spray volume of droplets smaller than 100 µm), RSF, and droplet velocities were measured with a particle/droplet image analysis system. Results showed that the wear resistance of nozzles with ceramic and polymer tips was five- and two-times higher than that of the stainless-steel tip. For all nozzles, the wear led to increased droplet size spectra (increased RSF), V₁₀₀ values and droplet velocities, indicating reduced spray uniformity and magnified drift potential. Overall, the nozzle wear significantly altered spray atomization and droplet dynamics, emphasising the need for regular nozzle inspections and timely replacement to maintain the intended spray quality. Furthermore, these results would provide valuable, comparable information to support manufacturers in designing innovative wear-resistant nozzles.