Experimental Study On Deposit Motion Of Charged Droplets When Approaching Target Leaf

During the deposition,the movement behavior of charged droplets will change when approaching the target leaf: under the action of electric field,the charged droplets around the leaf will move towards the leaf,and their trajectory will deflect to a certain extent.In plant protection operation,it is difficult for the droplets to enter the middle and lower parts of the canopy due to the shielding of the top leaves of the crop canopy.The deflection characteristics of charged droplets can improve the limitations,and further improve the deposition effect of droplets at different heights of crop canopy.By analyzing the literature,it is found that most of the current researches focus on the deposition effect of droplets on the back of leaves and in the middle and lower part of canopy to reflect this phenomenon,while few researches focus on the movement behavior of charged droplets when approaching the target leaves.There are also few studies on the interaction effects of charge parameters,spray parameters and canopy structure on the penetration of charged droplet crown deposits.Based on the above two points,this paper carried out the related research:(1)The charged droplet generator was set up and its charging performance was measuredThe principle and advantages of the commonly used droplet charging methods were compared and analyzed.According to the subsequent test scenarios and requirements,the induction electrostatic atomization system was established.The charge to mass ratio of the system is measured,and the charge to mass ratio under different charging parameters is obtained.The experimental results show that when the spray pressure is 0.5 MPa and the charging voltage is 10 k V,the optimal charge to mass ratio of charged droplets can be obtained by using the electrostatic positive output unit,which is 4.27 m C/kg.The results of variance analysis show that both the polarity of output cell and the charging voltage have significant effects on the charge mass ratio of charged droplets.(2)Distribution of number of charged droplets on the back of target leaf during depositionTaking three kinds of crop leaves as deposition targets,the number of droplets in the back area of the leaves at different times during the movement of droplets to the target leaves was observed.From the point of view of droplet group,the effects of static and non-static on the number of droplets on the back of leaf during deposition were analyzed.The results showed that the number of droplets in the back area of the three leaves increased under electrostatic spraying compared with non electrostatic spraying.The results showed that: compared with non electrostatic spray,during electrostatic spraying,the number of droplets on the back of basil leaf(leaf inclination is-10°)increased by 21%;the number of droplets on the back of cucumber leaf(leaf inclination is 30°)increased by 32%;the number of droplets on the back of chill leaf(leaf inclination is 45°)increased by 113%.This shows that the droplets will move towards the back of the leaf under the action of static electricity.(3)Study on the movement behavior of a single charged droplet when approaching the target leafTaking three kinds of crop leaves as deposition targets,the movement behavior of a single charged droplet approaching the target leaves was observed by using a highspeed image acquisition system.By using neighborhood matching method and charged droplet tracking method,the pixel value coordinates of charged droplets at four times when approaching the target leaf are marked,and the approximate motion trajectory of charged droplets is described.Furthermore,the two-dimensional coordinates of charged droplets approaching chilli leaf were obtained by camera calibration.According to the position information of charged droplets at different times,the influence of droplet size on its motion speed and deflection degree is analyzed.The results show that: among the three characteristic droplets studied,the smallest droplet A(11.25 pixels)has the largest horizontal velocity of 66.37mm/s and the smallest deflection angle difference of-0.163.When approaching the leaf,the smaller the droplet,the stronger the electrostatic effect,the greater the velocity in the horizontal direction,the smaller the difference of velocity deflection angle at different times,and the more obvious the trend of moving towards the leaf.(4)Experiment on deposition effect of charged droplets at different heights of tomato canopy1)The effects of two kinds of operating parameters on spray pressure and charged voltage on the deposition at three heights of top,middle and bottom of tomato canopy were studied by using single factor experiment.The results showed that the deposition efficiency of tomato canopy at three heights was significantly enhanced with the increase of spray pressure and charged voltage.2)Taking the coefficient of variation of droplet deposition coverage at the top,middle and bottom of tomato canopy as the index,the effects of different combinations of experimental parameters on the uniformity of droplet deposition at different heights of tomato canopy were studied.The experimental results show that when the spray pressure is 0.6 MPa and the charge voltage is 5 k V,the deposition uniformity of three droplets of the tomato canopy is 0.3488,which is the best among all parameters.The results also showed that spray pressure,charged voltage and interaction effect had significant effects on the uniformity of droplet deposition at three heights of tomato canopy.