Research On Orchard On-line Mixing For Air-assisted Variable Rate Spray System

Safe and efficient application of pesticides is important for orchard practices. At present, in generally level of plant protection machinery and pesticide application technology in China is low. Spray is still labor intensive, low effective utilization of pesticides and high environmental pollution. Air-assisted sprayer can generate high-speed air jets by means of fan and improve the transport and mixing of spray droplets for better coverage and deposition. On-line mixing technology can achieve real-time regulation of the concentration of spray liquids by avoiding a close contact between the operator and pesticide solutions, which is important for variable spraying technology. In order to optimize the spraying performance of orchard air-assisted sprayer, anon-line mixer for variable-rate spraying system was developed. This work conducted the design of mixing control system, development of key components and performance test using the numerical simulation and experimental demonstration methods. The main research work and conclusions are as follows:A prototype of mounted orchard on-line mixing for air-assisted variable-rate sprayer was developed, which can realize on-line mixing and variable-rate spray at the same time. Due to the individual control ability of the on-line mixing module combining peristaltic pump with static mixer and the variable-rate spray module including a tractor speed measurement unit, it can precisely inject variable pesticide solutions simultaneously to meet the requirement of different pesticide applications. The variable-rate spray can be achieved according to the tractor speed and size of tree crown. Using a STM32 chip as the core of the controller, the control system consisted of power unit, water control unit, pesticide control unit, wireless communication unit, data storage unit, tractor speed measurement unit and crown detection unit, which could meet the demands of cooperative control for on-line mixing and variable-rate spray.Based on 3-D model of three insert-type configurations of static mixers named SK, SX,SD type and computational fluid dynamics, the internal velocity fields, turbulence kinetic energy and the second phase volume fraction in the mixing process of three mixers were characterized and quantified using FLUENT software with the SIMPLEC algorithm and k-? model. Simulation results show that the SX static mixer had several mixing advantages compared to other mixers and its optimal number of mixing unit was 5.In the on-line mixing experiments, the glycerin was substituted for pesticide along with adding carmine stain. It was found that the mixing test results of SX static mixer were in good agreement with the simulation results, which would provide a reference for the application of orchard on-line mixing operation.The pesticide flow control had rapid response since the response time were 0.3s and 0.28 s from 24ml/min step to 108ml/min and resumed from 108 ml/min to 24 ml/min. The results of mixing stability test showed that the maximum errors between the actual concentration and reference concentration were less than 4.33%. Moreover, the coefficient of variations of mixing homogeneity were no larger than 4.98%.The results showed that on-line mixing module can meet the demands of the orchard sprayer.The results of tractor speed measurement test showed that the maximum errors between the actual speed and reference speed were less than 1.97%. Moreover, the maximum errors between the actual crown volume and reference crown volume were less than 15.4% by setting the correction factor value as1.15. In the case of driving speed of2km/h and 4km/h during variable rate spray module test, the maximum errors between the actual flow and reference flow were less than 15.4%.The results showed that variable-rate spray module can basically meet the performance requirements.