Reduced span spray – Part 2: Drift

Treatment efficiency is drastically affected by the amount of spray drift away the target area.
The present study investigates the effect of a reduced span on spray drift based on wind tunnel
measurements with the final aim of guiding the design of a reduced span nozzle (Reduced
span spray – Part 3: Design of narrow span nozzle). A capillary jet with a free and a forced
break up regimes, corresponding to 0.5 and 0.06 span values respectively, was tested under 2
m/s downwind speed. Droplets spots from the free break up regime show a bimodal
distribution, which are related to droplets sizes: Bigger droplet travel less distance than
smaller droplets. Droplet diameters measured on ground level at different distances from the
generator were corroborated with the observed droplets spots. However, deposits from forced
break up regime were similar to deposits obtained by the free break up regime, what may be
due to emerged drops throughout the droplet stream. Much focus on the forced break up
regime is needed to relate droplet size to spray drift.