脉宽调制变量控制喷头雾化性能及风洞环境雾滴沉积特性
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摘要
脉宽调制(pulse width modulation, PWM)技术是实现变量喷雾的重要手段,其工作参数与环境条件决定着施药的精准性。为探究PWM变量喷头雾化及风洞环境沉积特性,该文研制了脉宽调制变量喷雾系统,以农业施药常用空心圆锥雾化喷头喷雾的雾化、沉积特性为研究对象,在IEA-II型常规风速风洞内,通过点阵式放置电容式雾滴沉积传感器测定计算雾滴沉积与沉积评价指数(deposition evaluation index,DEIX),并利用Spraytec雾滴粒径仪测试其雾滴体积中径(volume median diameter,VMD)和雾滴相对分布跨度(relative span,RS)。试验结果表明:占空比在10%～40%间,随占空比增大,雾滴体积中径呈减小趋势,与占空比10%时相比,占空比40%时的雾滴体积中径下降了7.9%;PWM占空比60%时分布跨度最小,较占空比20%时雾滴分布跨度下降9.52%,雾滴谱最窄,获得的雾滴粒径分布最集中。雾滴沉积方面,风速1 m/s条件下,雾滴主要沉积在距喷头3.3 m内,此范围内沉积量占总沉积量的95.7%,当风速超过3 m/s时,在气流作用下,雾滴沉降距离增大,导致雾滴运动偏离施药靶标区域。PWM占空比增加,雾滴沉积评价指数DEIX值降低,雾滴的飘移率增大;相同工况下,风速及喷头高度越大,DEIX越小,施药雾滴越易飘移。该研究可为农业田间实际生产中脉宽调制变量施药技术应用及其工况参数的选择提供依据,为PWM变量调节装置的进一步优化提供研究基础。
Pulse width modulation(PWM) technology is an important means to achieve variable spray,and is attracting more and more researchers' attention due to its short reaction time,fast response,large flow adjustment range and good spray characteristics using conventional nozzles.But during the actual spraying process,its working parameters and environmental conditions could influence the spray accuracy seriously.In order to investigate the atomization and deposition characteristics of the PWM variable-rate nozzle,a pulse width modulation variable spraying system was designed to study the spraying atomization and deposition characteristics of TR80-005 C hollow cone spray nozzle commonly used in agricultural application.In order to maintain a stable environmental condition to produce setting wind speed,the experiments were carried out in the type IEA-II wind tunnel designed by Agricultural Intelligent Equipment Technology Research Center.A dot matrix placement capacitive droplet deposition monitoring sensor was used to detect spray deposition in real time.To effectively evaluate the ground deposition properties of the wind tunnel environment,deposition evaluation index(DEIX) was deduced based on drift potional index(DIX).DEIX is inversely proportional to DIX,the smaller the DEIX value,the smaller the potential of droplet deposition,which means that the possibility of drift loss is greater.The Spraytec droplet size meter was sued to test the droplet volume median diameter(VMD) and the relative span of the droplets(RS) to determine the relationship between duty cycle and spraying atomization performance.The experiment was carried out at the Xiaotangshan National Precision Agriculture Research Station in Changping district of Beijing city.The test devices were mainly composed of PWM variable-rate spraying system,IEA-II conventional-speed wind tunnel,laser particle size analyzer and deposition measurement sensor network system.Before tests,all systems were powered on and warm up for 30 minutes.In the droplet size tests,the nozzle was placed 0.5 m directly above the droplet size analyzer,the test pressure was set to 0.4 MPa,the PWM frequency was set to 1 Hz,and the duty cycle was set to 10%-60% at the interval of 10%.Tap water was used as the spraying solution,and each setting repeated 5 times.For the droplet deposition characteristic tests,droplet deposition sensor was arranged at the bottom of the wind tunnel,the sensors were arranged in 5 rows(1 m spacing) and 3 columns(0.55 m spacing) on the vertical wind direction,and were numbered 1 to 15 starting from the upper side to the bottom of the upper side.The nozzle was fixed at the top of the wind tunnel,and the height of the relative deposition sensor was set to 1 and 1.5 m respectively,and the horizontal distance between the nozzle and the first column deposition sensor was 1.3 m,the wind speed was set to 1-5 m/s,PWM frequency was set to 1 Hz and duty cycle was 10%-60%,spraying time was set as 10 s,the spraying pressure was set as 0.4 MPa.At the beginning of the test,the sensors saved datas in real time and transmitted it back to the computer.The test results showed that when the duty cycle was between 10%-40%,the VMD decreased with the increases of duty cycle,VMD was 122.3 μm at 60% duty cycle,which increased by 1.8 μm compared with that of at 40% duty cycle.When the PWM duty cycle was 60%,the RS was the smallest,compared with that of duty cycle at 20%,the RS decreased by 9.52%,that means that the droplet spectrum was the narrowest,and droplet size distribution was the most concentrated.In the deposition test,under the condition of wind speed at 1 m/s,droplets were mainly deposited within 3.3 m from the nozzle,which accounted for 95.7% of the total deposition.When the wind speed exceeded 3 m/s,the droplet settling distance increased under the action of the airflow,which may increase the possibility of spray drift.With increase of the duty cycle,DEIX value decreased and the drift rate of the droplets increased.Under the same working conditions,the larger the wind speed and the nozzle height,the smaller the DEIX and the easier spray drift.This study provides a basis for the practical application of pulse width modulation variable application techniques and PWM working condition parameters selection in agricultural field production,and provides a theoretical basis for further optimization of PWM variable adjustment devices.
Pulse width modulation(PWM) technology is an important means to achieve variable spray,and is attracting more and more researchers' attention due to its short reaction time,fast response,large flow adjustment range and good spray characteristics using conventional nozzles.But during the actual spraying process,its working parameters and environmental conditions could influence the spray accuracy seriously.In order to investigate the atomization and deposition characteristics of the PWM variable-rate nozzle,a pulse width modulation variable spraying system was designed to study the spraying atomization and deposition characteristics of TR80-005 C hollow cone spray nozzle commonly used in agricultural application.In order to maintain a stable environmental condition to produce setting wind speed,the experiments were carried out in the type IEA-II wind tunnel designed by Agricultural Intelligent Equipment Technology Research Center.A dot matrix placement capacitive droplet deposition monitoring sensor was used to detect spray deposition in real time.To effectively evaluate the ground deposition properties of the wind tunnel environment,deposition evaluation index(DEIX) was deduced based on drift potional index(DIX).DEIX is inversely proportional to DIX,the smaller the DEIX value,the smaller the potential of droplet deposition,which means that the possibility of drift loss is greater.The Spraytec droplet size meter was sued to test the droplet volume median diameter(VMD) and the relative span of the droplets(RS) to determine the relationship between duty cycle and spraying atomization performance.The experiment was carried out at the Xiaotangshan National Precision Agriculture Research Station in Changping district of Beijing city.The test devices were mainly composed of PWM variable-rate spraying system,IEA-II conventional-speed wind tunnel,laser particle size analyzer and deposition measurement sensor network system.Before tests,all systems were powered on and warm up for 30 minutes.In the droplet size tests,the nozzle was placed 0.5 m directly above the droplet size analyzer,the test pressure was set to 0.4 MPa,the PWM frequency was set to 1 Hz,and the duty cycle was set to 10%-60% at the interval of 10%.Tap water was used as the spraying solution,and each setting repeated 5 times.For the droplet deposition characteristic tests,droplet deposition sensor was arranged at the bottom of the wind tunnel,the sensors were arranged in 5 rows(1 m spacing) and 3 columns(0.55 m spacing) on the vertical wind direction,and were numbered 1 to 15 starting from the upper side to the bottom of the upper side.The nozzle was fixed at the top of the wind tunnel,and the height of the relative deposition sensor was set to 1 and 1.5 m respectively,and the horizontal distance between the nozzle and the first column deposition sensor was 1.3 m,the wind speed was set to 1-5 m/s,PWM frequency was set to 1 Hz and duty cycle was 10%-60%,spraying time was set as 10 s,the spraying pressure was set as 0.4 MPa.At the beginning of the test,the sensors saved datas in real time and transmitted it back to the computer.The test results showed that when the duty cycle was between 10%-40%,the VMD decreased with the increases of duty cycle,VMD was 122.3 μm at 60% duty cycle,which increased by 1.8 μm compared with that of at 40% duty cycle.When the PWM duty cycle was 60%,the RS was the smallest,compared with that of duty cycle at 20%,the RS decreased by 9.52%,that means that the droplet spectrum was the narrowest,and droplet size distribution was the most concentrated.In the deposition test,under the condition of wind speed at 1 m/s,droplets were mainly deposited within 3.3 m from the nozzle,which accounted for 95.7% of the total deposition.When the wind speed exceeded 3 m/s,the droplet settling distance increased under the action of the airflow,which may increase the possibility of spray drift.With increase of the duty cycle,DEIX value decreased and the drift rate of the droplets increased.Under the same working conditions,the larger the wind speed and the nozzle height,the smaller the DEIX and the easier spray drift.This study provides a basis for the practical application of pulse width modulation variable application techniques and PWM working condition parameters selection in agricultural field production,and provides a theoretical basis for further optimization of PWM variable adjustment devices.
引文
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[2]张波,翟长远,李瀚哲,等.精准施药技术与装备发展现状分析[J].农机化研究,2016,4:1-5.Zhang Bo,Zhai Changyuan,Li Hanzhe,et al.Development status analysis of precision pesticide application techniques and equipments[J].Journal of Agricultural Mechanization Research,2016,4:1-5.(in Chinese with English abstract)
[3]刘慧,夏伟,沈跃,等.基于实时传感器的精密变量喷雾发展概况[J].中国农机化学报,2016,37(3):238-244.Liu Hui,Xia Wei,Shen Yue,et al.Development overview of precision variable spraying based on real-time sensor technology[J].Journal of Chinese Agricultural Machanization,2016,37(3):238-244.(in Chinese with English abstract)
[4]袁会珠,杨代斌,闫晓静,等.农药有效利用率与喷雾技术优化[J].植物保护,2011,37(5):14-20.Yuan Huizhu,Yang Daibin,Yan Xiaojing,et al.Pesticide efficiency and the way to optimize the spray application[J].Plant Protection,2011,37(5):14-20.(in Chinese with English abstract)
[5]薛新宇,兰玉彬.美国农业航空技术现状和发展趋势分析[J].农业机械学报,2013,44(5):194-201.Xue Xinyu,Lan Yubin.Agricultural aviation applications in USA[J].Transactions of the Chinese Society for Agricultural Machinery,2013,44(5):194-201.(in Chinese with English abstract)
[6]Womac A R,Melnichenko G,Steckel L E,et al.Spray tip configurations with pulse-width modulation for glufosinateammonium deposits in Palmer amaranth(Amaranthus palmeri)[J].Transactions of the American Society of Agricultural and Biological Engineers,2017,60(4):1123-1136.
[7]邓巍,丁为民,何雄奎.PWM连续变量喷雾的雾滴速度和能量特性[J].农业工程学报,2009,25(增刊2):66-69.Deng Wei,Ding Weimin,He Xiongkui.Droplet velocity and energy characteristics of continuously variable spray based on pulse width modulation[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2009,25(Supp.2):66-69.(in Chinese with English abstract)
[8]何雄奎.改变我国植保机械和施药技术严重落后的现状[J].农业工程学报,2004,20(1):13-15.He Xiongkui.Improving severe draggling actuality of plant protection machinery and its application techniques[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2004,20(1):13-15.(in Chinese with English abstract)
[9]张东彦,兰玉彬,陈立平,等.中国农业航空施药技术研究进展与展望[J].农业机械学报,2014,45(10):53-59.Zhang Dongyan,Lan Yubin,Chen Liping.Current status and future trends of agricultural aerial spraying technology in China[J].Transactions of the Chinese Society for Agricultural Machinery,2014,45(10):53-59.(in Chinese with English abstract)
[10]邱白晶,闫润,马靖,等.变量喷雾技术研究进展分析[J].农业机械学报,2015,46(3):59-72.Qiu Baijing,Yan Run,Ma Jing,et al.Research progress analysis of variable rate sprayer technology[J].Transactions of the Chinese Society for Agricultural Machinery,2015,46(3):59-72.(in Chinese with English abstract)
[11]邱白晶,李坤,沈成杰,等.连续可变量喷雾系统响应特性试验[J].农业机械学报,2010,41(9):32-35.Qiu Baijing,Li Kun,Shen Chengjie,et al.Experiment on response characteristics of variable-rate continuous spraying system[J].Transactions of the Chinese Society for Agricultural Machinery,2010,41(9):32-35.(in Chinese with English abstract)
[12]Gonzalez R,Pawlowski A,Rodriguez C,et al.Design and implementation of an automatic pressure-control system for a mobile sprayer for greenhouse applications[J].Spanish Journal of Agricultural Research,2012,10(4):939-949.
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