Optimization of the inner flow channel of conical wind field anti-drift spray device and anti-drift characteristics

Abstract: An anti-drift sprayer with a conical wind field has emerged as an innovative structural device for the auxiliary airflow in plant protection operations during crop production. There is also a significant reduction of droplet loss for the effective deposition of fine particles in the target areas. However, an airflow obstruction can be found in the flow channel of the current sprayers, leading to the lower overall performance of the device. In this study, a systematic optimization was made on the inner flow channel in an anti-drift spray device under a conical wind field, thereby clarifying the anti-drift mechanism for better performance of the device. A force model of a single droplet was also constructed for the moving air medium, according to proton dynamics. After that, the CFD numerical simulation and wind field test were utilized to optimize the airflow loss in the inner runner for the better design of the device. The simulation result showed that the disturbance of eddy current was improved without the abnormality of local speed after optimization. Specifically, the conical wind speed at the outlet of the device still reached 17.00 m/s, increasing by 23.5%, compared with that before the optimization. The wind speed test showed that the effective utilization rate of the auxiliary airflow at the outlet of the device was 21.2 percentage points higher than that before the optimization, when the radius of curvature of the inner flow channel elbow was designed to be 4 cm, indicating that the optimization plan was feasible. Furthermore, there were significant correlations between the cross wind speed, nozzle height, conical wind speed, and the proportion of total droplet drift under wind tunnel conditions. By contrast, there was a negative correlation between the conical wind speed and the proportion of total droplet drift. More importantly, the proportion of the total droplet drift presented a downward trend, whereas, the adverse effect of the crosswind on the droplet deposition gradually decreased, with the increase of conical wind speed. Additionally, a multi-factor orthogonal experiment was carried out to establish the mathematical model of the total droplet drift ratio in the vertical/horizontal direction. It was found that the cone-shaped wind field significantly reduced the droplet loss in the space with the wind. There was also a higher significance of the vertical/horizontal mathematical model (P<0.05, R2 was 0.934 in vertical and 0.945 in horizontal, respectively). Consequently, the conical wind field can be widely expected to effectively resist the generation of vortexes, thereby reducing the droplet loss with the wind in the vertical height. This finding can also provide a sound reference for the comprehensive analysis of droplet migration and deposition in protected agriculture.