Research On Technique To Reduce Spray Droplets Drift

High volume spraying is widely applied with large droplets in china. Low volume spraying technology was researched by the way to improve the efficiency of small size droplets and control spray drift. The factors, which affect the spraying drift, were analyzed and the characteristics of droplet drift were tested and evaluated in wind tunnel. In view of the presented researchs and technology in drift control, a shield sprayer with air stream guiding system was developed to reduce the drift. Furthermore, the droplets trajectory and deposit were simulated by Fluent software to analyze the principle of anti-drift spraying with double-foil shield sprayer. The key parameters of double-foil shield were optimized and comparative trials of anti-drift were done in wind tunnel to evaluate the different shields structure.The characteristics of droplet drift and deposit were tested in the comparative trials with representative nozzles at different wind speeds, temperatures, relative humidity etc. DIX, an index to evaluate the droplet drift of spraying parts, was introduced here. The results showed that both droplet size and the meteorological conditions affect the drift, whereas the droplet size and wind speed were the key factors. In different wind-tunnel conditions, the drift using a low-volume standard fan nozzle Lechler 110015 was much more than that of Lechler 11003, which is a high-volume nozzle.Double-foil shield is a high-efficiency and non-driven mechanism for preventing droplet drift, and the effect of anti-drift is depended on the guiding air curtain. Three conclusions about the anti-drift principle of double-foil shield with guiding air were achieved by simulating. (1) the air curtain is a airstream movement in a small area, and the guiding air curtain with more extensive area has more effect on the fluent field below the wind exit. Therefore the droplets were intimidated to deposit down to the area under nozzles by increasing the wind speed in vertical direction.(2) When the guiding air curtain had the horizontal velocity, which opposites to the direction of the fluent field below the wind exit, then the droplet horizontal velocity would be reduced to improve the droplets deposition, thus drift could be lessened. (3) Extending the function area of the guiding air curtain would also reduce the droplet drift.Based on the analysis of simulated test and the compare of performance, a new air-guide shield was designed. The wind entrance width was 0.3 meter , and the exit width of the wind curtain is 0.15 meter with a 15° -forward-tilt air-guide wing. By the simulated tests and comparative trails in the wind-tunnel, the anti-drift efficiency and the performance of old air-guide shield, new air-guide shield and conventional non-shield under different conditions were studied. The result showed that both of the air-guide shields markedly reduced the droplet drift, which was consistent with the result of wind-tunnel trails. In addition, the reduced drift ratio to spraying volume of the new one was twice or more times than that of the old one. So the improvement of the shield was feasible, and the analysis of the anti-drift principle with air-guide shield was correct.The distance to the centre of mass of the spray deposit (Dc) was used to evaluate the droplets drift. The distance character of droplet deposit and distribution was evaluated by using the index of Dc, thedistance of the deposit droplet center, with the new shield, a good efficiency of anti-drift was achieved with low-volume nozzle Lechler 110015 and high-volume nozzle Lechler 11003, while the Dcof the latter was less than that of the former. Moreover, the Dc was greater in higher air pressure and lower air speed than in lower air pressure and higher air speed, which indicates that the pressure had more effect on Dc through the change of droplet size than the wind speed. Therefore, the air-guide shield was better for the droplet intimidation sedimentation than other shields.