Research On Air-assisted Spray System Based On Annular Jet Technology

Plant protection operation is an essential link in agricultural production.Manual spraying is time-consuming and laborious,and it is difficult to operate on tall fruit trees and close planting crops,which has great limitations.Air-assisted sprayer is a widely used plant protection machinery.It has become the properties of wide range and strong penetration.This device effectively promotes the efficiency of plant protection and reduces labor intensity.However,the existing air-assisted sprayer has many problems such as complex structure,heavyweight and poor spray uniformity.Based on this,this paper explores the application of annular jet technology to the air-assisted sprayer for air supply operation,so as to simplify the structure of the air-assisted sprayer and improve the quality and safety of the spray operation.The work of this paper is as follows(1)Through the study of the annular jet technology and the existing air-assisted spray system,a new design scheme of the air-assisted spray is put forward.That is,the annular jet technology is used to design an air supply mechanism,with which can generate a uniform flow field with several times larger air flow,and fit the mechanism with the spray parts,such as nozzle,and so on,thus obtaining a set of spray system with simple structure,high quality and strong security.(2)Based on the flow field shape,outlet air flow and wind speed,the influence of pressure,outlet angle and section distance on the air supply performance of annular jet mechanism were studied by adopting two-dimensional fluid simulation method.By comparing the simulation results under different pressures,it is found that the pressure mainly affects the velocity and air flow at the outlet,but has no effect on the shape of flow field.When the internal pressure is 2500 Pa,the wind speed at the outlet is close to10m/s,which can accomplish long-distance air supply.The outlet angle has a significant effect on the shape of the flow field and the size of the air flow.The flow field generated by the annular jet mechanism with the outlet angle greater than 90° is unstable.When the exit angle is less than 90 degrees,the steady flow field can be obtained,and the wind speed and air volume of the flow field generated by the annular jet mechanism with 30°and that of 60° exit angle are larger.Different section distances have no effect on the shape of the flow field,and the air flow of the outlet remains close,but with the increase of the section distance,the velocity of the exit decreases.(3)Orthogonal experiments were carried out on four factors which affect the air supply performance of annular jet mechanism,including section distance,diversion angle,outlet angle and gap width.The results show that the gap width is the most important factor affecting the air flow,and the optimal factor level is 1.7mm;the priority of the other three factors is different under different indicators.In the optimal level of factors,the optimal level of outlet angle is 30°,the optimal level of section distance is 110 mm or140mm,and the optimal level of diversion angle is 12° Or 14°.In the case that the orthogonal experiment failed to determine the optimal combination of each factor,four groups of experiments with 2 × 2 were conducted.The width of the gap is set at 1.7mm and the outlet angle is 30°.The section distance is 110 mm and 140 mm,and the diversion angle is 12° and 14°.The results show that: the air flow obtained by the four groups of experiments is similar,but when the cross-section distance is 110 mm and the diversion angle is 12°,the wind speed generated by the annular jet mechanism are larger.That is to say,the best parameters of the cross-section of the designed annular jet mechanism are:gap width 1.7mm,diversion angle 12 °,outlet angle 30 ° and cross-section distance110 mm.Considering that in the follow-up experiments to explore the working relationship between the annular jet mechanism and the nozzle,enough space is needed.Finally,the annular jet mechanism is processed with a section width of 140 mm.(4)Adjusting to the actual needs,the three-dimensional model of the annular jet mechanism is designed.The size of the mechanism is 140 mm × 120 mm × 860 mm,while the height of the jet ring goes 800 mm and the height of the inlet duct goes 60 mm.The simulation results show that the flow field generated by the designed annular jet mechanism has the problems of uneven distribution of outlet air flow,disordered direction and concentrated bottom pressure.Thereafter the optimization of annular jet mechanism is completed by adding guide structure and baffle in the model.Taking the velocity size and the uniformity of velocity distribution as the index,the air supply performance of the annular jet mechanism is tested through field experiments.The experimental results show that: the variation of wind speed on the horizontal axis is consistent with the simulation results,and the error of wind speed is between 3.2% and 16.2%;the velocity distribution in the vertical direction at different distances from the exit of the annular jet mechanism is uniform,with the error of the simulation results between 1.3% and 14.7%.(5)A spray nozzle commonly used in orchards was selected for spraying.The parameters such as spray angle,flow rate,mist distribution and droplet size were measured under different pressures.The experimental results showed that with pressure,the spray angle and flow rate of the nozzle gradually increasing,the droplet size decreased.When the pressure is 0.6MPa,the spray angle can be close to the maximum spray angle specified by the nozzle.Under this pressure,the width of nozzle spray is 0.72 m,the current speed is 4.36L/min,the coefficient of variation of spray distribution of single nozzle is 52.3%,and the median particle size reads 110.7 μm.(6)The performance of the air-assisted spray system consisting of the nozzle and the annular jet mechanism and the related supporting devices is tested by experiments.The experimental results show that under the entrance pressure of 1000 Pa,the spray distance is 5.7m,which is higher than that without wind assisted.In addition,the air spray system based on annular jet technology can increase the coverage of droplets.At 3m from the exit of the annular jet mechanism,the coverage rate of droplets under the auxiliary air supply state is 59.07%,while the coverage rate of fog drops is 35.36% in the absence of wind.When matching the nozzle with the annular jet mechanism,the spray effect is better at the rear of the annular jet mechanism than in the front and inside,but the distance between the nozzle and the annular jet mechanism can not be greater than 17.5cm when located at the rear.