| As an environment-friendly spray method,air-assisted electrostatic spray has been paid more and more attention by researchers.At present,it has been widely used in aviation,orchard,field and other scenes.However,there are still few studies on the application of air-assisted electrostatic spray technology in the greenhouse of tomato.In this scene,the charged characteristics of the droplet moving to a long distance and the droplet deposition law become the focus of the research.In this paper,the sprayer for greenhouse based on single hanging track is used as the spray carrier to explore the charged characteristics of droplets under different parameters,and provide guidance for the design and working parameters selection of electrostatic spray in greenhouse.The main research contents of this subject are as follows:(1)Design and produce device for charge measuring.When the spray pressure is0.3 MPa and the induced voltage is 6 k V,the charge mass ratio is measured at the distance between the electrode and the measuring device at 0.1,0.2,0.3,0.4 and 0.5 m respectively,and the uncertainty reaches 0.4%～1.5%;Comparing the measured value of charge mass ratio with Faraday cylinder,the minimum difference of 3.5% occurs when the distance between the electrode and the measuring device is 0.3 m.(2)For the flat fan nozzle,the effects of different parameters on droplet charging are studied,including the distance between electrode and nozzle,electrode spacing,induced voltage and wind speed.The results show that:(a)the peak current reaches 2.5μA when the electrode spacing is 20 mm and the distance between electrode and nozzle is 6～10 mm.The development of air-assisted electrostatic nozzle is based on this.(b)When the induced voltage is in the range of 1～7 k V,the charge mass ratio of droplets increases with the increase of voltage,but beyond this range,the charge mass ratio decreases.(c)Increasing the wind speed can effectively improve the charge mass ratio of droplets.In the voltage range of 1～7 k V,the charge mass ratio of droplets increases with the increase of wind speed.After the voltage reaches 7 k V,the greater the wind speed,the more obvious decrease of droplet charge mass ratio.(3)The effects of spray distance and wind speed on the charge mass ratio of droplets were investigated,and the charge attenuation law of droplets during movement was obtained by direct measurement.When the spray pressure is 0.3 MPa and the charging voltage is 7 k V,the variance analysis results show that the distance,wind speed and their interaction have a significant impact on the droplet charge mass ratio.The attenuation of surface charge of droplets under the action of external electric field and air flow is theoretically analyzed and experimentally verified.(a)The method of establishing droplet charge attenuation model is proposed.The wind speeds at the outlet of the fan are 14.5,23 and 31.2 m/ s respectively,and the model parameters k are 47.84,14.52 and 4.17 respectively.The larger the value of k is,the slower the droplet surface charge attenuation deceleration rate is.(b)The correlation between the electric field intensity and the change rate of droplet charge is analyzed to verify the effect of electric field on the attenuation of droplet charge.The correlation coefficient R obtained from the two factor correlation analysis is greater than 0.8,which shows that there is a significant correlation between the electric field intensity and the change rate of charge.(4)The air-assisted electrostatic nozzle is installed on the greenhouse sprayer,and the spray deposition test is completed.Using the Box-Behnken method,the induced voltage,spray pressure and the angle between nozzles were taken as the experimental factors.The response index was the coverage rate of droplets on the target at 1,3 and 5m of the nozzle.The results showed that:(a)the significant order of the influence of each factor on the droplet coverage rate on the target at 1 m is: the angle between the sprinklers,the spray pressure and the induced voltage.The significant order of the influence of each factor on the droplet coverage rate on the target at 3 m is: spray pressure,the angle between the sprinklers and the induced voltage.The significant order of the influence of each factor on the droplet coverage rate on the target at 5 m is:spray pressure,the angle between the nozzles and the induced voltage.(b)The determination coefficients of the regression model of droplet coverage relative to the target at the distance of 1 m,3 m and 5 m from the nozzle are 95.41%,89.88% and91.56% respectively.(c)Compared with the predicted value of the model,the relative errors of the droplet coverage relative to the target at the distance of 1 m,3 m and 5 m from the nozzle are less than 11%,7% and 15% respectively.The predicted value of the model has high reliability. |
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