Study On Deposition And Wetting Of Spray Liquid On Plant Target

The deposition and wetting of spray liquid on the target plant is an important link, which will decide on liquid pass to the organism. The dynamic wetting conditions will directly impact on the liquid droplet deposition, attachment, retention, distribution and infiltration, etc. As the spray is a dynamic process, the dynamic wetting behavior of liquid droplets on the target plant is an important factor of affecting spraying efficiency. Taking the barbette model pressure atomization axial-flow air-carried high-voltage electrostatic spraying system as the experiment platform, the parameters of droplets motion and deposition in the state of induction charge were measured and analyzed. Using water, alkyl polyglycoside(APG 08-10), glyphosate additives (EF 8108-B) as pesticide adjuvants, and using lettuce, cucumber growing in greenhouse as the plant target, the process of dynamic wetting on the plant leaf surface were visually observed and recorded. Especially, the experimental study on wetting property and the mechanism for spreading of pesticide adjuvants solutions on the live plant leaf surface were carried out and investigated. This study will offer theoretic and technologic bases in analyzing or predicting the dynamic wetting of pesticide spraying adjuvants solution on plant target.The main research works in the paper are as follow:1. To study the range of pesticide droplet deposition and droplet distribution in different target district and plant target by axial-flow fan of the air-carried blast sprayer in greenhouse, spraying experiment were tested with variable height of nozzle and charged voltage under the same condition of spray pressure, spray flux and frequency of fan. Taking the barbette model pressure atomization axial-flow air-carried high-voltage electrostatic spraying system as the experiment platform, the parameters of spraying deposition on target were calculated and analyzed. The results showed that one deposition peak area was found along the wind cylinder axes when the distance was 150-200 cm form nozzle; With the increasing voltage, pesticide droplet deposition on plant target increased obviously. The percentage of toward-target deposition rose distinctly within range of spraying after the state of induction charge. To adjust height of nozzle and charged voltage were important measures for adding toward-target depostion depending on the practical target of spraying application. 2. In order to understand the wetting property of alkyl polyglycoside (APG 08-10) aqueous solution on the surface of live plant leaf, the gas-liquid interface equilibrium surface tension of APG aqueous solutions were measured with pendant drop method. The process of dynamic wetting on the surface of cucumber leaf was visually observed and recorded by using CCD camera and the digital image technique. The time-dependent and the concentration-dependent spreading performances of APG aqueous solutions on cucumber leaf surface were investigated, too. The results showed that the dynamic contact angles were multiform and random in different concentration APG solutions mass fraction range from 14.35% to 85.78%. The relationship spreading diameter vs. time accord with power theorem and all of the power were lower than 0.1.3. To research the mechanism for spreading of glyphosate additives (EF 8108-B) aqueous solution on the cucumber leaf surface, the process of spreading was described and recorded by high-speed digital camera technology. The dynamic contact angle, drop size and drop shape of different mass fraction of EF 8108-B range from 16.08% to 82.14% were measured and the data was analyzed by curve fitting method. The results showed that the change trend of dynamic contact angle did not increase with concentration.22.33% aqueous solution concentration of EF8108-B on cucumber leaf surface showed better spreading performance. Either positive or back on the cucumber leaves, dropl height with different concentration of system aqueous solution on cucumber leaf decline rapidly within the first 2 s, and then decreased slowly and gradually to reach its stabilized. With time increases, dropl area of the different concentration of system aqueous solution on the leaf surface decrease whole, but some drop area with other concentration appears slightly elevated.4. Based on time series prediction analysis method, EF8108-B solution on cucumber leaves of various types of dynamic wetting models were established. According to self-relevant and self-regression method, the mobile average method and exponential smoothing method, these models were constructed, respectively. Including dynamic contact angle model, dynamic droplet size model and dynamic droplet shape model. Moreover, three-dimensional curves of droplet size, droplet shape and contact angle were simulated. With trend surface theory analysis methods, three-dimensional dynamic contact angle trend surface model were built, and the related parameters were analyzed and calculated. It shows that these models reach a certain reliability and accuracy according to the experimental observations data. 5. To study the point of run-off and maximum retention the of spray liquid on cucumber leaves in greenhouse, the spraying experiment were tested with variable charged voltage and spray volume. The parameters of retention volume on cucumber leaves surface were measured by micro-weighing method. The factors of affecting the retention volume on cucumber leaves were analyzed based on basic theory of Young's equation, including spray distance, droplet contact angle and spray volume. The experimental results showed that with the increasing distance, point of run-off and maxium retention rises firstly and then declines; the contact angleθ, adhesion forceβ, adhesion work Wa, critical surface tension y0 is 85.07°,6.17 mN·m-1,77.97 mJ·m-2, 61.23 mN·m-1, respectively. Less than the critical surface tension of cucumber leaves was conducive to the liquid wetting and deposition on cucumber leaves.6. In order to evaluate of retention the of spray liquid on spraying target, the point of run-off charged pesticide droplet per area on cucumber leaves was investigated with orthogonal test including parameters such as the electrostatic voltage, spraying pressure, spraying flow and nozzle height. The results show that electrostatic voltage, spraying flow and the spraying pressure have significant effects on leaf target. The respective correlations between the point of run-off on cucumber leaves and electrostatic voltage or spraying pressure were investigated under two single factor experiments. The main effects and interactions of these two factors were conducted by the 2 factors and 5 levels central composition design. Results show that the two main effects on point of run-off were significant and their interaction had little effects under the criterion. A second-order regression equation based on response surface methodology was fitted to data and was used to provide the optimized scales of both voltage and pressure. The application of response surface methodology is an effective method for conducting a reduced number of experiments in order to obtain the optimum spraying conditions to achieve the desired specifications of the point of run-off. The optimization parameters are that spraying pressure range from 0.25 to 0.55 MPa and electrostatic voltage range from 20 to 40 kV, respectively.