摘要
研究雾滴在树冠内的分布规律,对优化喷雾参数,提高喷雾效果有重要意义。该文以叶密度、出口风速和取样深度为试验变量,用试验法研究了树冠内雾滴穿透比例分布规律;试验结果表明:雾滴穿透比例随叶密度、取样深度的增加而减小,随喷雾机出口风速的增大而增大,其中取样深度对穿透比例影响最为显著。在此基础上,结合试验数据与统计学方法,构建了雾滴穿透比例二次指数数学模型,并确定了模型的待定系数,其模型精度R^2高于0.95,经检验模型有一定的合理性和可靠性。基于此模型,计算了雾滴冠后飘移率,与实测值相比,平均相对误差为16.73%。进一步对雾滴冠后飘移率影响因素、双面喷雾机理、喷雾参数优化进行了分析,拓展了模型应用,对模型局限性和进一步优化模型的后续研究设想展开了说明。研究对风送喷雾雾滴分布规律研究具有一定的参考价值。
Understanding droplet distribution inside tree canopy has a great significance on optimizing spray parameters and improving spray effect.In this article,distribution of droplet penetration rate inside tree canopy during air-assisted spraying was studied by experimental method.The droplet penetration rate was defined as the ratio of droplets inside canopy along unit vertical face to that before penetrating into the canopy.The change of droplet penetration rate with tree leaf density,outlet air velocity of sprayers and sampling depth was analyzed.Disc sprayer and multi air pipe sprayer were used to spray 4 types of tree canopies of pear trees(big,medium and small sizes),wintersweet,cerasus subhirtella and punica granatum.Droplet deposition was determined in real time.The results showed that the droplet penetration rate decreased as the leaf density and sampling depth increased while it increased with increased outlet air velocity of sprayer.Among the 3 test variables of tree leaf density,outlet air velocity of sprayer and sampling depth,the sampling depth greatly affected the droplet penetration rate.Following the changing pattern of droplet penetration rate with tree leaf density,outlet air velocity of sprayer and sampling depth,5 types of models(linear polynomial,quadratic polynomial,cubic polynomial,single exponent and quadratic exponent)were assumed to fit the changing pattern of droplet penetration rate.The quadratic exponent model had the highest accuracy with R2 higher than 0.95 and the RMSE was the least from 4.1%to 5.0%.By experimental validation,the model still had relatively reliable accuracy.Thus,the quadratic exponential model was finally chosen as the suitable model.By using this model,it had to be built based on canopy of each tree.By mixing the data from different tree canopies,we tested the feasibility to estimate droplet penetration rate by a quadratic exponential model.The results showed that the R2 was still higher than 0.95 and root mean square error was 5.3%-5.7%.By validation,the relative error could be lower than 20%for mixture of wintersweet,cerasus subhirtella and pear trees but reach up to about 29%for punica granatum tree.It was because the branch structure of punica granatum was different from the other trees.The quadratic exponential model was then extended to application in calculating droplet drift rate after tree canopy in order to analyze its influencing factor.The droplet drift rate after Cerasus subhirtella tree canopy of different leaf density under different sprayer outlet air velocities was calculated using model and validated by test.The mean relative error was 16.73%,indicating that the model could be used to determine the suitable outlet air velocities for tree canopies of different growing stages and reduce the droplet drift rate.The variation coefficients of droplet distribution inside tree canopy were also calculated by the model,which was used to better explain the principle of double-side spraying pattern.In the end,the model limitation and subsequent research assumption to improve model were illustrated:spray pressure,flow rate,environmental temperature and humidity were approximately regarded as constants in this article,and in further researches,the influence on droplet penetration rate of these factors should be investigated.A unit model for estimating droplet penetration rate could be established if the tree types had similar branches and leaf structures,and in further researches,more types of trees should be chosen and classified to build mixture model to improve the model accuracy.This paper is helpful to understanding droplet distribution in tree canopy during air-assisted spraying.
作者
孙诚达
柳长鼎
Sun Chengda;Liu Changding(College of Mechanical and Electrical Engineering,Shaoxing University,Shaoxing 312000,China;College of Engineering,Nanjing Agricultural University,Nanjing 210031,China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2019年第15期25-32,共8页
Transactions of the Chinese Society of Agricultural Engineering
基金
浙江省基础公益研究计划项目“雾量在线测量系统的设计及其关键技术研究”(LGN19C140004)
关键词
喷雾
雾滴
模型
冠层穿透
spraying
droplets
models
canopy penetration
