Experimental Study And CFD Simulation Of Air-assisted System On Super-high Clearance Boom Sprayer

Pest control for high-stalk crops, like corn and sugarcane, at their middle and late growing stages, has remained a problem over years in China. It is therefore of great theoretical and practical value to study anti-drift technology of pesticide droplets for the development of crop protection equipment and effective application practice for pest control over the entire growth period of high-stalk crops.This study is part of the Study on Efficient Application of Pesticide and Development of Sprayer for High-stalk Crops (project number:2008AA100901), a project funded under the National High-Tech R&D Program (or863Program). Experiment, design and performance optimization of a high-penetrable air-assisted system were conducted on super-high clearance self-propelled boom sprayer, modeled3WZC-2000, developed through the project. Experimental study and CFD simulation were focused on the distribution characteristics of deposited droplet and the law of droplet drift during the application of pesticide in high-stalk crops with the high-penetrable air-assisted system.A new type of air-assisted system was designed with the speed and direction of air flow adjustable so that the operational parameters could be regulated in real time for improved pesticide utilization and reduced environmental pollution.Simulating model of air-velocity distribution of air-assisted system was developed based on the standard k-ε turbulent model, then the structure of air-assisted system was optimized, As a result, the optimized exit flow speed of the air-assisted system was increased, and the assisted air flow was uniformly distributed along the direction of boom, resulting in improved system performance.Field experiments were conducted on the pesticide application technology of high penetration in the super-high clearance boom sprayer at the corn height of0.8m,1.6m and2.2m respectively, in order to study the influence of spraying pressure, working speed of sprayer, air speed at the outlet of air-assisted system, and characteristics of plant canopy on the deposit rate and the uniformity in distribution of droplets. The system performance in anti-drift and pesticide utilization was analyzed.The results of field experiments showed that the assisted air flow from air-assisted system on the super-high clearance boom sprayer had a strong penetrability by evidence that the droplets deposited on the middle and lower plant canopy of high-stalk crops increased significantly during the pesticide application; the assisted air speed was positively correlated to the distribution uniformity of droplets deposited. The higher the speed of air at the outlet of the system was, the more uniform the deposited droplet was distributed and the stronger the penetrability of droplets was; Given that all the working conditions remained unchanged, the deposition of droplets on unit canopy area would be increased with the spraying pressure, while the uniformity of droplet distribution did not vary obviously. Among the four factors that affected droplet deposition and uniformity of droplet distribution, the air speed at the outlet of the air-assisted system played a determinant role, followed by canopy characteristic, spray pressure and working speed of the sprayer. The air-assisted system of the super-high clearance boom sprayer had been proven to be highly effective in controlling the droplet drift and improving the pesticide utilization efficiency.A droplet deposition and drift distribution model was established for high-penetration air-assisted pesticide application in accordance with the actual structure of the sprayer, using the CFD software Ansys Fluent, adopting the Discrete Phase Model (DPM), standard k-ε turbulence model and Couple algorithm. The simulation test was designed using Central Composite Design to study the relationship of drift rate with its influencing factors. The functional relation of droplet drift rate with its influencing factors at different rotation speed of blower fan was established and the accuracy of the simulation result was validated, indicating that the model was well fitted.In order to achieve the least droplet drift, reasonable value ranges were worked out for the rotation speed of blower fan, the angle of air-assisted flow and the horizontal installation position of spray nozzles at the Beaufort wind scale1,2,3and4, respectively.