Experimental Study On Collision And Condensation Of Pesticide Drops In Crop Target Interface

Chemical control has become the only effective way to control plant diseases and insect pests.The use of pesticides can alleviate the infection of plant diseases and insect pests and reduce the loss of food.However,in the process of pesticide application,rough application is widely used,which can not accurately grasp the dynamic information of splashing,rebound,coagulation and spreading after the droplets hit the leaves of plants,resulting in high input of pesticides,poor target pertinence,and poor spreading and wetting of the liquid on the surface of leaves.In view of the above problems,deltamethrin pesticide is selected to spray on the surface of two kinds of common target crops.The surface tension,dynamic contact angle,spreading diameter,adhesion tension,adhesion work and other characteristic parameters of the drug drops on the surface of the leaves are measured by the optical contact angle measuring instrument.The collision and coagulation process of the drops on the target crop leaves are mainly studied,and the pesticide solution is analyzed.The relationship between the surface tension,the characteristic parameters of liquid medicine on the blade surface and the free energy of the blade surface.The trend of dynamic contact angle,the lag of contact angle,and the effect of collision and coalescence on the effect of application were discussed.The main results are as follows:(1)analysis of change trend and hysteresis of contact angle of target surfaceThe static contact angle of deltamethrin drops on six parts of the leaf surface of water spinach was measured,and the range of static contact angle was(40.10～60.9°).In plant protection operation,the influence of the morphological characteristics of each part of the leaf surface on the application effect should be fully considered.For the leaf surface with small roughness,uniform leaf surface and relatively flat,the contact angle lag is small,and the application process is conducive to the spread of the droplets on its surface.The closer the free energy between the liquid medicine and the leaf surface is,the better the liquid medicine can spread on the leaf surface of water spinach and reduce the liquid medicine loss effectively(2)the aggregation behavior of deltamethrin emulsion drops on the leaves of water spinachUnder the condition of plant protection,the coagulation time and superposition effect of droplets on the target leaves should be fully considered.The contact angle of the new droplets can be reduced by 12.9%when the new droplets are combined by rolling into the bottom suction mode.It can be concluded that the over spreading behavior caused by surface tension gradient is better than that driven by dynamic surface tension.It is beneficial to spread the liquid medicine on the leaf surface of water spinach.The suitable application mode should be selected according to the leaf position and characteristics of the target,which can effectively reduce the liquid medicine loss(3)vertical impact test of deltamethrin emulsion dropletsThe equal volume of 5 μL deltamethrin drops was used to stack on the surface of spinach leaves.When the distance between adjacent drops is 1≤0.69 mm,the single direction impact of the drops will coalesce with the adjacent drops.When the distance between adjacent drops is 1≥0.77 mm,the single direction impact of the drops will not coalesce with the adjacent drops.The contact angle of the new droplets formed by colliding with the adjacent droplets in one direction decreases by 28.33%～40.5%;the contact angle of the new droplets formed by colliding with the adjacent droplets in the middle space decreases by 24.69%～35.93%;the contact angle of the new droplets formed by colliding with the adjacent droplets in one direction increases by 6.47%-14.2%.In the surrounding area.It is found that the distribution,spacing and density of the group droplets in the process of spraying should be fully considered,as well as the superimposed coagulation time on the target leaf surface.(4)the interface behavior of deltamethrin emulsion droplets impinging on tilted target cropsWhen the collision rate of droplets is 0.0826 M/s,there are three kinds of phenomena,that is,direct suction at the top,suction at the top and roll at the bottom.The contact angle difference of the new droplets formed by the way of rolling into the bottom suction is reduced by 3.9%;the adhesion tension and adhesion work after collision is greater than that before collision,which is conducive to the spreading of the liquid medicine on the leaf surface of water spinach.It was found that there were many interspace between veins in the A3 part of water spinach.The effect of interspace between veins on the application effect should be fully considered in the actual plant protection work.