| At present,the control of diseases and insect pests mainly depend on chemical prevention and control,of which the field application is mainly carried out through the sprayer.Because of the low utilization rate of pesticides in the process of operation,the waste of pesticides and environmental pollution are caused.Therefore,under the background that reducing pesticide and chemical fertilizer are proposed by the government,airflow assisted spray technology has developed rapidly with advantages of high efficiency and drug saving.In this paper,by studying the principle of airflow assisted secondary atomization,a cone-shaped airflow assist device is designed on the basis of the F-110 series fan-shaped nozzle produced by Danish HARDI.Besides,the influence degree of various factors is obtained by exploring the performance of the cone-shaped airflow auxiliary device and the influence law on the spray quality,thereby reducing the drift of mist droplets and improving the utilization rate of pesticides.The main results of this study are as follows:(1)A conical air flow assisted spray device was designed by analyzing the principle of air flow assisted secondary atomization.Besides,the gas-liquid two-phase flow field at the air outlet was simulated by Fluent software,and the movement trend of the droplet group under the coupling of natural wind and cone-shaped auxiliary air flow was analyzed.Combined with high-speed photographic analysis,the theory of secondary atomization of fog droplets was verified.(2)The particle size of droplet was measured by laser particle size meter.Through the single-factor and multi-factor orthogonal test of the influence of spray pressure,spray flow rate and auxiliary airflow velocity on the particle size of fog drops,the effect of various factors on the droplets particle size was explored under different working conditions.The fitting results of the test data by SPSS statistical analysis software are as follows: the spray flow rate(nozzle type)is the main factor,followed by the spray pressure and the flow rate of the auxiliary airflow,which are negatively correlated with the droplet size.Under the action of auxiliary airflow,the average diameter of spray droplet volume of each type of nozzle decreases about 10 ?m,and the reduction range is 5.7% to 8.4%.Through the analysis of the droplet size spectrum of the droplet,the average particle size of fog drops decreased by 8.82 ?m at 400 mm below the nozzle,indicating that the auxiliary airflow can play the role of refining the droplets and homogenizing the mist field.(3)An air-assisted spray droplet drift test system was set up to conduct experimental research on the droplet drift characteristics under the action of the conical air flow auxiliary device.The effect of the natural wind and the cone-shaped auxiliary airflow on the droplet drift rate and drift center distance Law of influence was explored.The test results show that the drift rate decreases by 40.35% to 59.14% and the drift center distance decreases by 55.26% to 60%after increasing the conical auxiliary air flow compared with the traditional spraying method.(4)A mobile spray test bench suitable for this study was built.Through single factor and response surface orthogonal test,the influence degree and change law of various operating parameters and environmental parameters on the droplet deposition characteristics was investigated.The results indicate that the influence degree of each factor is cone wind speed,natural wind speed and spray pressure.When the natural wind speed,the spray pressure and the conical wind speed are 2 m/s,0.34 MPa and 16.53 m/s,respectively,the optimal droplet deposition amount is obtained.Besides,the deposition coverage rate,the deposition density and the deposition volume are increased by 21.9%,26.71%,and 22.6% under the action of conical auxiliary airflow,which prove that the auxiliary airflow can effectively improve the spray quality. |
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