Experimental Investigation Of Droplet Characteristics And Drift Performance In Air-assist Boom Sprayer

Air-assist boom spraying technology is a research which focuses on the field of plant protection.Air-assisted flow pressures droplets to the crop canopy deposition,it can effectively reduce the droplet drift,which increases the efficiency of pesticide application,reduces the ground loss rate,enhance the droplet penetration,promote droplets deposition uniformity and application safety.Domestic study of air-assisted boom sprayer has just started, mainly focusing on machine integration and the realization of air-assisted function. Based on the domestic and foreign study of drift reduction technology and droplet characteristics for air-assisted boom sprayer,the relationship between the droplet characteristics and drift in the air-assist boom sprayer were studied by experiments. The research work of this paper are as follows:(1) An air-assist boom spraying and measuring system was developed with gas-liquid two-phase flow.This test system is mainly composed of the laser particle size analysis system, PIV analysis system and the collection spray test equipment.The air-assist boom spraying test rig is composed of the air-assist and the spray control system.(2) The droplet diameter of air-assist boom spraying field were tested and analyzed in various conditions using Winner318 laser particle size analyze.The analysis and discussion combined the effect of the three parameters by the test: at different spraying pressure for different wind speed with various distances between the nozzle and the target.Experimental results showed that when the spray height from300 mm to 700 mm,the spray pressure is the main factor affecting the droplet size distribution, with the increase of spray pressure, the droplet diameter becomes smaller;at different air-assisted flow velocity, the droplet diameter with the spray height variation trend consistent, with the increase of the air-assisted flow speed, the droplet diameter becomes higher, the droplet diameter decreases gradually;the same spray condition, when the spray height increases, the droplet diameter increases.(3) The droplet velocity of air-assist boom spraying field were tested and analyzed in various conditions using PIV analysis system,we can use PIV analysis system to analyze the droplet movement velocity and vorticity distribution in flow field.Experimental results showed that the spraying pressure has a significant impact on the droplet velocity and vorticity distribution,with the increase of spraying pressure,the droplet velocity becomes higher,the large scale eddy dissipationgradually,the vorticity distribution becomes smaller.In air-assisted flow action, the droplets velocity distribution were more uniform.Uniformity of the droplets movement velocity also is proportional to the spraying pressure, the spraying pressure from 0.2MPa to 0.5MPa, the droplets movement velocity in the vicinity of 2m/s largest number, and after 2m/s the number of droplets is also showed a trend of increasing with the spraying pressure, the droplets movement velocity distribution uniformity is increased with the increase of the spray pressure better.(4) The study of spray drift for air-assisted boom sprayer was experimented in the laboratory, through a comprehensive test, analysis of the spraying pressure,air-assist flow speed and spray height,the test was used to contrastively analyze the affection degree of three influence factors on anti-drift performance of air-assist boom spraying and analyze the quantitative relationship between influencing factors and the droplet deposition.Experimental results showed that increase the spraying pressure,the trend of the droplet drift rate decreased slowly;when air-assist flow speed from0m/s to 10.3m/s,it can effectively reduce the droplet drift rate,air-assist flow speed exceeds the 10.3m/s,the droplet drift performance decreased significantly.The spray height has great influence to the droplet drift rate and considers the influence of air-assist flow action at the same time, when the spray height is less than 400 mm,air-assist flow is bigger, the drift droplets larger;from 400 mm to 600 mm, with the increase of the nozzle and target distance, the droplet drift trend gradually weakened;When distance is larger than 600 mm, because the air-assist flow effect is abated, the droplet drift rate trend is not obvious.Affect the droplet drift performance of air-assist boom spraying is that the degree of air-assist flow speed and spray height;a group of optimal parameters about drift performance in Air-assist boom spraying as follows: the spray pressure is from 0.2MP to 0.5MPa, the fan frequency30 Hz, spray height from 400 mm to 600 mm, nozzle vertically downward.