Simulation of Spatial Trajectory and Regulation of Chemical Pesticide Droplets
The use of chemical pesticides is extremely indispensable for pest and disease control in crop protection and agricultural production. However, due to the fact that most of the actual operations are based on human long-term experiences without enough theoretical guidance, particle drift and evaporation drift always occur under the action of current after droplets are released from nozzles. The effectiveness of the pesticide operation is still significantly limited by the spray technology and management. According to the statistics provided by professional organizations, the pesticides utilization efficiency is only 20-30% and spray drift can pose a considerable threat to bystanders, residents, livestock, even terrestrial and aquatic ecosystem. In this study, in order to explore the evolution laws of droplets motion and predict the particle drift ratio influenced by multiple factors in the current, a computational fluid dynamics (CFD) model is used to track the spatial trajectory of the droplets cloud through varying surface tension (0.035N/m-0.1N/m), viscosity (0.001Pa·s-0.1Pa·s), diameter and velocity distribution, wind velocity (1-5m/s), spray height (0.5m-1.0m). Multiple regression analysis and multi-objective optimization are integrated to obtain the optimal spray parameter combination and ensure adequate coverage on intended canopy, so as to lower the spatial loss of chemical pesticides. It shows that increasing surface tension and viscosity of pesticide solution can make nozzle produce more larger droplets with better performance of resisting entrainment, which can have a reducing effect on drift ratio. Spray height can cause greater impact on deposition velocity of droplets falling on canopy leaves than deposition diameter. And impacting droplets with higher velocity are prone to jump off the canopy target, also causing loss of chemical active components. Simultaneously, the optimal spray application is recommended with the wind velocity of 1-3m/s. This study demonstrates that CFD model can be used to evaluate the spray application performance in field operation. More importantly, it can provide a beneficial concept to regulate the current spray application technique and design an optimal scheme with lower drift ratio and higher coverage on intended target.