Agricultural sprays in cross-flow and drift

The droplet size and velocity characteristics of an agricultural spray were studied in a wind tunnel in the presence of a non-uniform cross-flow. The spray was generated at three nozzle-operating pressures. The droplet size a nd velocity was measured in both the cross-flow direction and the vertical direction using a phase Doppler particle analyser. From the size-velocity measurements, it was found that many droplets immedi ately behind the spray sheet were found to be travelling in a direction opp osite to the cross-flow. Further away from the nozzle, some small droplets had a velocity directed upwards. A size-velocity correlation factor was ado pted to discuss the potential drift of the droplets. For the lower pressure , at a distance of 100 mm below the nozzle exit, the droplets are prone to drift at all downstream locations. dt the higher pressure, the droplets are prone to drift beyond a distance ratio (x/z) of two. Here, x is the distan ce in the cross-flow direction and z is the vertical distance below the noz zle exit. The behaviour of droplets of two particular size classes ( simila r to 38 and 70 mum) were also investigated and found that the smaller dropl ets were subjected to an increased cross-flow effect. (C) 2001 Silsoe Resea rch Institute.