| Crop protection is the main way to control crop diseases and insect pests.Especially,it has the guiding significance to do the research of the relationship between droplet movement and plant leaf surface.Therefore,a piezoelectric single droplet generator suitable for crop protection area is proposed to produce the droplets with the diameter of 50~300?m.Meanwhile,the influence factors of the droplet size are studied in this paper and the work effect of the single droplet generator is evaluated by the actual droplet size.The design idea of piezoelectric single droplet generator is put forward in this paper.And also it study the working effect of the generator based on piezoelectric actuator vibration model analysis and image processing technology.Its specific research has the following four aspects:(1)Design and manufacture of the piezoelectric single droplet generatorFirstly,the physical model of the piezoelectric actuator is established and the size of the piezoelectric actuator is also designed in the piezoelectric single droplet generator.When the driving frequency input is 30 Hz and the voltage input is in the range of 50~80V and use trapezoidal wave in the 0.16 mm nozzle,the generator can produce the droplet of 0.15~0.28 mm and meet the design expectations.(2)Making numerically simulation of the injection process of a single droplet by the fluent module in ANSYS14.5 It researches the influence of the flow field,velocity field and pressure field about falling droplet through the VOF model in ANSYS14.5.Then,it compiles the UDF to study the influence of sinusoidal signal in the droplet formation.And it is found that the internal velocity and pressure of droplet are adjusted all the time.It finally reaches a dynamic balance when the velocity and pressure are uniformly distributed inside the droplet and the droplets fall evenly.At the same time,the droplet falling process is divided into five stages: stretching growth,necking half moon shape,liquid column breakage,droplet drop oscillation and droplet pelletizing.(3)The vibration model analysis of piezoelectric actuatorFour driving waveforms are input into piezoelectric actuators by arbitrary wave signal generator to study the effect of the input waveforms on the vibration of piezoelectric actuators.And the experiments use the laser displacement sensor measurement to measure the vibration displacement of piezoelectric actuators.It is found that the trapezoid waveform is suitable for single droplet generator.It's also found that the condition of the droplet can fall off from the nozzle are the maintained time of trapezoidal wave high level.It is also found that the formation of the droplet is truly had five stages in the trapezoidal wave and it verified the results of the simulation stated above.(4)Influencing factors of the droplet size(1)It is found that the error rate of MATLAB image processing method is less than 7% and lower than the high-speed camera software processing when compared the method of droplet diameter measurement with high-speed camera software and MATLAB image processing;(2)It is found that the effect of nozzle length to diameter ratio is small.However,the droplet diameter increases with the increase of nozzle diameter and the nozzle length to diameter ratio through establishing the fitting curve of droplet diameter and nozzle parameter;(3)It's found that the droplet size increases with the increase of voltage amplitude at 50~80V in the effect of the voltage input amplitude.But the droplet size decreases due to the increase of the piezoelectric input frequency at 30~80Hz;(4)It's found that the droplet size increases with the increase of input pressure and the drop velocity.However,if the pressure is too large,the input pressure will replace the vibration of piezoelectric actuator and make the droplet form the jet;(5)It is found that satellite droplets will be produced when the droplet diameter is larger than 1.9 times the size of the liquid column. |
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