Droplet Size and Velocity Characteristics of Agricultural Sprays

The quality of agricultural sprays plays an important role in the application of plant protection products. For 13 nozzle-pressure combinations, droplet size and velocity characteristics were measured 0.50 m below the nozzle using a PDPA laser-based measurement setup. Nozzles were mounted on a transporter to sample the whole of the spray fan. The effects of nozzle type (standard, low-drift, and air-inclusion), nozzle size (ISO 02, 03, 04, and 06) and operating pressure (2.0, 3.0, and 4.0 bar) were tested. Measured droplet sizes and velocities were related, and both were affected by nozzle type, size, and operating pressure. Droplet velocities at 0.50 m were determined by their size and initial ejection velocity. In general, bigger droplet sizes correspond with higher droplet velocities, and smaller droplets with lower droplet velocities. Important differences in velocities were observed depending on the nozzle type and size, both affecting the ejection velocity. For the same droplet size, droplet velocities were highest for the flat-fan nozzles, followed by the low-drift nozzles and the air-inclusion nozzles (because of the lower ejection velocities caused by pre-orifice and Venturi effects). Similarly, the bigger the ISO nozzle size, the faster were the droplets of the same size. Droplet velocities of the larger droplet sizes (>400 µm) varied from about 4.5 to 8.5 m s-1 depending on the nozzle type and size. Below 400 µm, droplet velocities consistently decreased with the decrease in droplet size, and vary from 0.5 to 2 m s-1 depending on the nozzle type and size. All this information is very useful with regard to crop penetration, the risk of spray drift, and the quantity and distribution of the deposit on the target.

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