Study On Pesticide Drift Reduction Strategy Based On Droplet Size Spectrum Regulation

When applying pesticides in the field,the liquid medicine will form a group of droplets with different sizes and high-density distribution after atomization by the nozzle.The droplets with smaller sizes are easy to drift with the wind due to the entrainment of the environmental wind field,resulting in the loss of pesticide dose and the destruction of the ecological environment,which greatly reduces the utilization rate of pesticides.In this paper,according to the basic national demand for reducing the amount of pesticide application and improving the utilization rate in the process of pesticide spraying,by building a multi-functional test platform for droplet spatial distribution,taking the droplet size spectrum and droplet drift deposition as the evaluation indicators,the droplet drift behavior is regulated from the two perspectives of spray source and droplet spatial trajectory,and the average drift reduction rate of the regulatory scheme under different operating parameters is quantified.Firstly,the influence of spraying parameters on the initial distribution of droplet spectrum is explored.By testing the spatial distribution of droplet size of different types and models of nozzles,it is found that for hollow cone spray and plane fan-shaped spray.The droplet size in the middle area of spray is small,and in the peripheral area is large.For TR,ST,and IDK nozzles of the same model selected in this paper,there is little difference in volume medium diameter of droplets between TR and ST nozzles.IDK nozzle belongs to air induction nozzle.The droplets formed after atomization contain gas,so the droplet particle size is the largest.For the test of spray pressure,with the increase of spray pressure,the volume median diameter of droplets decreases,and the volume proportion of easily drifting droplets increases.Secondly,the drift-reducing performance and anti-drift regulation mechanism of functional spray adjuvants are analyzed.It is clear that the anti-drift control mechanism of spray adjuvants is to prolong the initial atomization process of the liquid film by changing the physicochemical properties(viscosity and surface tension)of the liquid,including the two physical processes of the liquid film stretching into liquid filaments and the liquid filaments breaking into droplets,so as to realize the control and optimization of the droplet size spectrum,specifically to increase the volume median diameter of the droplets and reduce the volume proportion of the easily drifting droplets.For TR nozzle and ST nozzle,vegetable oil adjuvants BEIDATONG,MAIFEI,MAIRUN,ND 800 and silicone adjuvant Silwet 806 all have excellent anti-drift effect.Among them,0.1% MAIFEI adjuvant has the best anti drift effect on TR nozzle,and the average anti-drift rates in horizontal and vertical directions can reach 55.23%and 65.90% respectively;The drift rate of the nozzle in the vertical direction can be reduced by52.0% and 54.0% respectively.From the test results of this paper,it is found that the anti-drift performance of the adjuvant is basically consistent with its improvement effect on the droplet size spectrum.IDK nozzle belongs to the anti-drift nozzle.Adding spray adjuvants to the liquid medicine has no obvious regularity on its anti-drift performance.Finally,the effects of the superhydrophobic spray baffle designed in this paper on the spatial behavior of droplets and the average drift reduction rate are discussed.Through the droplet spectrum measurement experiment,it is found that on the one hand,the superhydrophobic spray baffle improves the droplet spectrum uniformity of the TR nozzle and ST nozzle by 16.56% and 42.42% respectively,on the other hand,it increases the volume median diameter of droplets and reduces the volume proportion of easy drifting droplets.It shows that the setting of the spray baffle can promote the rebound process of fine size droplets and promote the collision and coalescence of these droplets with other sizes of droplets,The mass of fine size droplets was transferred to medium size droplets.In the test of droplet deposition and anti-drift performance,it is found that by setting the spray baffle,the drift of droplets outside the target area is reduced and the deposition of droplets inside the target area is increased.With the increase of ambient wind speed,the optimal baffle positions corresponding to TR and ST nozzles move to the upper layer of the wind tunnel,which further explains that the anti-drift control mechanism of the spray baffle is to bounce back the smallsize droplets that collide with the baffle surface,change their trajectory and improve the collision and convergence probability between them.The comprehensive test shows that the average drift reduction rate of the baffle to the TR and ST nozzles can reach 45.84% and 37.10%,which greatly improves the utilization rate of pesticides.