Study On Impinging Nozzle Based On The Coupling Of Jet And Impinging Jet

The problems of spray machinery and technology of nozzles are analyzed,and combined with the characteristics of impinging jet theory and the research status of impinging nozzle,it is proposed that the theory of impinging jet be applied to the development of plant protection nozzle technology.The invention involves a kind of impinging nozzle based on the coupling of jet and impinging jet,which overcomes the shortcomings of the flat-fan nozzle,such as wide droplet spectrum,poor droplet size uniformity,etc.It provides technical support for intelligent precision sprayers.Based on the analysis of the mechanism of jet atomization and impinging jet atomization,the atomization mechanism of the impinging nozzle is put forward.It is pointed out that three-atomization,which is disturbance,impact and oscillation,can improve the droplet size uniformity during the atomization process.And based on the analysis of the impinging jet spray device,a structure scheme of impinging nozzle based on the coupling of jet and impinging jet is proposed.Based on the working principle and structure scheme of the impinging nozzle and combined with product semantics,the product semantic model is proposed and the product opportunity is analyzed.The conceptual design of the impinging nozzle has been completed and has been authorized the national invention patent(201610858510.1)——the self-excited impinging nozzle.In view of the deficiencies of flat-fan nozzles in present use that spray droplets are wide and the droplet size uniformity is poor,an impinging nozzle is designed according to the assembling requirement of the experimental equipment,and a mathematical model of nozzle outlet determining droplet size distribution is derived.The characteristics of impinging nozzle manufacturing process are analyzed,and the trial production process,material and specific dimension parameters of nozzle sample are determined.Using rapid prototyping manufacturing technology,the flat-fan nozzle and the self-impinging nozzle were produced which have the same exit shape,exit diameter(1mm)and groove angle(30°).A mathematical model is established and FLUENT is used to analyze the characteristics of the internal and external flow of the jet nozzle.It is found that the maximum total pressure occurs about 0.3 mm from the nozzle inlet,when the velocity and flow reaches the maximum.The maximum turbulent kinetic energy and turbulent intensity along the nozzle axis occurs about 0.1 mm from the nozzle inlet,and the maximum turbulent kinetic energy and turbulent intensity is at the nozzle outlet near the inner side of the impact surface.After jet impingement,the velocity component of droplets in vertical downward(z axis)tends to be the same at the same horizontal height(e.g.,on the horizontal test surface 23 mm from the bottom of the nozzle body at 0.5MPa pressure,the velocity component of droplets is70.33-73.70 m/s),and decreases along the positive direction;the velocity component of droplets in horizontal direction(x axis)is small in the middle and large on both sides,and the velocity near the central axis is small and irregular;and the velocity component of droplets in front and back direction(y axis)is small.The velocity component of droplets in vertical downward is similar at the same horizontal height,and the droplet size will be homogenized by the impact of the jet,then droplets with uniform size will be generated in the spray field;and the velocity component of droplets in the horizontal direction will affect the spraying swath of the nozzle.A test bench is designed and built to study the atomization performance of the impinging nozzle.The droplet size and droplet distribution are measured by the spray performance test system.It is found that the impinging nozzle has the characteristics of narrow droplet spectrum and good droplet size uniformity(at the position 100 mm away from the nozzle exit,when the spraying pressure changed within the range of 0.3-0.8MPa,it was found that the S value of the distribution span of flat-fan nozzle and impinging nozzle were respectively between 1.73-1.90 and 1.07-1.17,and the spraying performance test system showed that the droplet were more concentrated,which indicated that the droplet size was better uniform and narrower spectrum);wide pressure regulating range and good anti-drift ability(the spray pressure ranges from0.6MPa to 0.8MPa,and the droplet size of the fan nozzle varies within 13?m at each test point,while the droplet size of the impinging nozzle exceeds 33?m);and the droplet size distribution in the spray field is uniform in the middle and smaller on both sides(e.g.,when the spraying pressure is 0.4MPa,the droplet diameters of the middle droplet are 265-268?m and the droplet diameters of both sides are 250-252?m on the test surface at the 300 mm height).The impinging nozzle overcomes the shortcomings of the flat-fan nozzle with wide droplet size and poor droplet size uniformity,and provides a feasible technology reference for the development of intelligent precision sprayers.In evaluating the droplet size uniformity in spray field,a new dimensionless index,Radial nonuniformity index,is used to quantitatively analyze the droplet distribution uniformity in spray field.It is found that the radial nonuniformity index can reflect the non-uniformity of droplet size in spray field on the whole.When the spraying pressure is 0.6-0.7MPa,the spray field of the impinging nozzle has relatively good droplet distribution uniformity.The droplet size is different at different positions in the spray field of flat-fan nozzles,which appears that the droplet diameter of the middle droplet is small and the droplet diameter of both sides is larger,which is close to the U-shaped distribution.This results in that the droplets in the overlapped area of the two adjacent nozzles are much larger than the droplets in the unoverlapped center area on boom sprayers.The uneven droplet size distribution of the spray field overlapped leads to the differences of the droplet deposition and the control effect on the targets at different points of the same height in the horizontal direction.The droplet size distribution in the spray field of the impinging nozzle is characterized by the uniform distribution of the middle and less distribution on both sides,which helps to improve the uneven distribution of droplet size distribution of the boom sprayer.The impinging nozzle based on the coupling of jet and impinging jets has certain significance for improving droplet size uniformity,precision spraying technology and improving the efficiency of spray machine.