风送式变量喷雾机气液两相流及雾化的试验研究
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摘要
传统的风送式喷雾机被普遍运用于果园病虫害防治作业中,喷雾机借助辅助气流的作用增加叶片间的扰动,提高雾滴的穿透能力,使得雾滴均匀粘附到叶片的表面,增大叶片表面覆盖率,确保高品质果品的产量,提高人们的生活水平。然而,传统的风送式喷雾机械不能根据树冠的大小和密度实时调整喷施量,进行针对性的精确喷雾,因此一旦喷雾机开始工作,就会按照设定的喷雾参数进行定量喷施,导致对靶标过量喷雾或者喷施量不足,以及对非靶标的误喷,从而产生对周围环境的污染。
风送式变量喷雾机能够在一定程度上解决传统的风送式喷雾机所存在的问题,能够根据靶标的具体结构参数调整药液的喷施量,变量喷施农药,从而实现有的放矢。未来变量喷雾机械的发展方向应是根据靶标的实际情况对辅助风速和药液喷施量同时实施变量控制。
本研究基于USDA-ARS-ATRU(美国农业部农业工程应用技术国家实验室)自主研发的新型五指风送式变量喷雾机。该喷雾机采用的五指风送式喷头将传统大的气流出口变成若干个小的圆柱形气流出口,可以提高雾滴的穿透性,改善气流在树叶密度较大的果树冠层内部的分布情况。该喷雾机对每个喷头药液输送端都采用PWM控制电磁阀的通断时间,单独控制每个喷头的药液流量。由于果树冠层各截面具体的结构特征参数显著不同,该喷雾机喷头的特殊结构对于果树每个区域的精密喷雾具有潜在的优势。目前该喷雾机已经实现了对靶标的有无、密度和大小变量喷施药液,然而,根据靶标的具体情况进行风速变量控制尚未实现。本研究采用调节风机进口内径以改变喷头出口风速的方法,探索根据靶标具体结构特征参数实现风速变量控制的可行性,为风送式变量喷雾机实施变量风速控制提供依据。
利用PWM控制电磁阀通断时间从而控制各个喷头药液流量的五指风送式喷头能够在变量工作条件下确保一致的雾滴粒径分布,这是实现根据靶标具体参数进行变量喷雾的前提条件。影响雾滴粒径大小的可控参数主要有电磁阀占空比、喷雾压力、喷头出口风速和喷雾药液物理特性。因此需首先研究该五指风送式喷头在这些相关变量参数影响下雾滴粒径的分布情况。雾滴粒径随着喷头出口气流速度、喷雾压力、喷雾药液特性的变化而变化。试验结果表明：在这四个变量中,喷雾压力对雾滴粒径大小的影响最大,其次是喷雾药液的物理特性,最后是喷头出口风速。对于给定的工作条件,当占空比为20%-100%时,雾滴粒径分布无显著变化,占空比为10%时,雾滴粒径分布波动较大,电磁阀占空比的切换频率是10Hz。为减少雾滴粒径在变量工作条件下有较大的波动,因此该喷雾机选择的工作条件是：保持喷雾压力恒定,占空比的工作范围为20%～100%。虽然风速对雾滴粒径的变化会有一定影响,但雾滴粒径在风速作用下的波动范围满足喷雾机变量作业要求。
为了检测该风送式变量喷雾机喷头出口气流的分布情况,通过调节风机进口内径(0.13m,0.15m,0.18m,0.34m)以改变喷头出口风速,并在不同行驶速度(0km/s,3.2km/h,4.8km/h,6.4km/h,8.0km/h)时,采用CTA风速测量仪检验该喷雾机在距离喷头出口不同远处(0.025m～3m)以及距离地面不同高度(0.2m～2m)处气流速度和动态气流压力的分布。喷头喷出气流在距离喷头出口0.027m处以500的扩张角喷射到空气中,距离喷头出口0.08m处单个五指风送式喷头相邻两喷口喷出气流开始混合。当喷雾机行驶速度为0km/h时,喷头出口气流速度随着风机进口内径的增大而增大,随着喷头出口距离的增大而按照双曲线函数关系递减。当喷雾机的行驶速度为3.2km/h～8.0km/h时,气流速度随着喷头出口距离的增大而减小,而动态气流压力在距离喷头出口(0～3m)范围内随着喷头出口距离的增大而缓慢增加。气流速度和动态气流压力随着风机进口内径的增大而增大。根据试验结果得知,通过改变风机的进口内径能够有效的改变喷头出口气流分布,并能够实现在给定的风机进口内径、给定的喷头出口距离所在的高度方向上气流分布均匀,表明了该喷雾机通过调节风机进口内径实现变量风速控制的可行性。当喷雾机行驶速度为3.2～8.0km/h,喷雾机行驶速度的变化对喷头出口气流速度和动态气流压力的分布无显著的影响。
在此基础上研究了该喷雾机在不同风机进口内径条件下,以一定的行驶速度经过果树时,喷头不同出口气流在果树树冠不同位置的分布情况。采用CTA风速测量仪,将传感器放置在冠层内部不同位置处,当喷雾机通过果树时,放置在冠层内部检测气流流速的传感器探测到气流分布呈脉冲形状。气流速度和动态气流压力随着冠层深度的增加而减少,且动态气流压力减少的幅度不如气流速度减少的幅度大。沿着高度方向(高、中、低)和喷雾机行驶方向(前、中、后)测量点的平均气流速度和平均动态气流压力分布基本保持一致。由此可以得知：该喷雾机沿着高度方向和喷雾机行驶方向在不同风机进口内径条件下,距离喷头出口相同远处冠层各区域内的气流分布一致。根据叶面积指数、树冠冠幅尺寸以及树冠内靶标的具体位置这三个参数组成的无量纲参数,建立了气流流速、动态气流压力与无量纲参数之间的指数关系。
实现变量喷雾的目的在于改善喷雾效果、提高喷雾效率、减少药液流失。为此研究了该喷雾机在不同占空比(20%-100%)、喷雾机行驶速度(3.2km/h,4.8km/h,6.4km/h)和风机进口内径(0.13m,0.18m,0.34m)等变量参数共同作用下,其在果树冠层内喷雾药液覆盖率以及沉降量的分布情况。对于给定的工作条件,冠层内喷雾覆盖率和药液沉积量随着风机进口内径和占空比的增大而增大,但是树叶密度和树冠外形尺寸也是影响喷雾覆盖率和药液沉积量的重要因素。随着喷雾机行驶速度的增大,喷雾药液覆盖率减少。对于给定的工作条件,区域内采样点的喷雾覆盖率均值沿高度方向和喷雾机行驶方向有微小的变化,但喷雾结果满足喷雾要求。同时,分别建立了喷头出口气流速度和喷雾覆盖率以及动态气流压力和喷雾覆盖率之间的关系曲线,喷雾覆盖率随着气流速度和动态气流压力的增大按照对数关系式增大。
根据喷头出口气流速度、动态气流压力与无量纲参数(由叶面积指数、叶面积指数、树冠冠幅尺寸以及树冠内靶标的具体位置组成)的指数关系,以及喷头出口气流速度、动态气流压力与喷雾覆盖率之间的对数关系,可以实现根据果树的特征参数估测冠层内气流速度和动态气流压力,然后推算出靶标位置点的喷雾覆盖率,根据喷雾作业对覆盖率的要求,再校准适当的气流风速,为未来风送式变量喷雾机实现风速变量控制提供理论依据。
The use of conventional air-assisted sprayer to apply pesticides has ensured production of high-quality fruits and ornamental nursery crops and enhanced our living standard. However, conventional air-assisted sprayers discharge constant air flows that are independent of tree size and foliage density. The air velocity profiles of these sprayers cannot be altered to uniformly deliver droplets to different plant canopies. In many cases, the air velocities are either too high or too tow and consequently, crops are either over sprayed or under sprayed. Another problem with the fixed air velocity patterns are off-target losses to the air and ground.
Variable-rate air-assisted sprayers that match spray outputs to target needs may be the solution to those problems associated with conventional sprayers. Development of future variable-rate sprayers should include a variable capacity control of both liquid and air flows to match tree canopy structures.
The cross section and foliage density of a tree vary throughout its entirety during the growing season. To accommodate this variability and achieve spray delivery, spray outputs should be tailored to each targeted section. An automatic air-assisted sprayer that implements five-port air-assisted nozzles to perform variable-rate spray outputs may have the potential to achieve this objective. This nozzle was developed to improve spray penetration and air jet velocity distribution inside dense nursery crops by dividing conventional large air jets into five small jets. The USDA-ARS-ATRU has developed the experimental air-assisted five-port sprayer to achieve liquid variable rates on tree occurrence, structure and foliage density. However, the mechanics to achieve variable air rates for this type of sprayer have not been developed. Also, to elucidate the mechanistic principles underlying air-assisted five-port nozzles in variable-rate applications, the magnitude of influence of the spray parameters on droplet size distributions first must be determined. Therefore, the objectives of this study were to investigate possible methods to achieve variable-rate air flow rates for this sprayer and to determine the effect of spray parameters and variable-rate air velocities on droplet size distributions. These objectives were used to form a basis for the future development of an automatic device to control air flow rates for variable-rate sprayers.
Design of the PWM-controlled, air-assisted, five-port nozzle with consistent droplet size distributions is the first step for the development of intelligent sprayers that have automatic variable spray output functions to match the variations in plant canopy structures. Parameters that influence droplet sizes from the nozzle include solenoid valve modulation rate, liquid pressure, air velocity discharged from the nozzle, and spray solution physical property. The effect of modulation rate, spray solution, air velocity, and liquid pressure on droplet size distributions produced from an air-assisted, five-port nozzle coupled with PWM solenoid valves were investigated. Droplet diameter consistencies varied with air velocity, liquid pressure, modulation rate, and spray solution physical properties. Among these four variables, droplet size was most affected by liquid pressure, followed by spray solution and then air velocity. Droplet diameters did not vary with modulation rates at20%～100%, but they were more variable at the10%modulation rate. The optimal conditions that minimize droplet diameter variations for variable-rate spray applications with the air-assisted five-port nozzle were to maintain a constant liquid pressure and to use modulation rate of20%～100%. However, droplet diameters also varied with air velocity, and this variation was accepted for the use of the air-assisted five-port nozzle in future automatic variable-rate sprayer development.
Unimpeded air jet velocities from the air assisted, five-port sprayer in an open field were measured at four heights above ground, seven distances up to3m from the sprayer outlets, and five sprayer travel speeds from0to8.0km/h. Air jet velocities were adjusted by changing the sprayer fan inlet diameter. Air velocities were measured with a constant temperature anemometer system coupled with hot-wire sensors. The air jets expanded at a50°angle and intersected with adjacent air jets at0.027m from the five-port nozzle. At a sprayer travel speed of0km/h, axial air velocities from nozzle outlets increased as fan inlet diameters increased and decreased as a hyperbola function as the distance increased. Variations in the peak air velocities and dynamic airflow pressures with the travel speeds of3.2to8.0km/h and heights of0.2to2.0m were insignificant. When the sprayer was in motion, own to air entrainment and air jet disturbance, the peak air velocities decreased and dynamic airflow pressures increased slightly as the distances from nozzle outlets increased. For all the parameters tested, the peak air velocities and dynamic airflow pressure decreased as the fan inlet diameters increased, demonstrating that changing fan inlet diameters achieved variable air flow rates with uniform air profiles.
Based on the conclusions of the air velocity distributions in an open field, this research was continued to determine whether variable air velocity distributions inside different sizes of tree canopies could be achieved by varying fan inlet diameters. Air jet velocities impeded by plant canopies were measured at various locations inside canopies of three different tree sizes and foliage densities. Tree heights were1.65,2.35and3.0m, and leaf area indexes were13.4,2.5, and1.5, respectively. Air jet velocities were adjusted by changing the sprayer fan inlet diameters and measured with a constant temperature anemometer coupled with hot-wire sensors. Peak air velocity and dynamic airflow pressure decreased with foliage density and canopy depth. For the0.34m fan inlet diameter, dynamic airflow pressure ratio of front portion to back portion of the canopies was8.0,1.5and2.6for Tsuga canadensis, Ficus benjamina and Acer rubrum, respectively. Similarly, the front to back peak air velocity ratio was8.55,1.59, and1.89times for T. canadensis, F. benjamina and A. rubrum, respectively. Variations were significant for peak air velocities and dynamic airflow pressures among the three different tree volumes and foliage densities. Increased fan inlet diameters from0.13to0.34m, increased average airflow pressure from0.4to0.8N/m2,0.8to1.5N/m2, and0.5to0.9N/m2inside canopies of T. canadensis, F. benjamina and A. rubrum, respectively. Therefore, alterations of fan inlet diameters for the five-port air assisted sprayer achieved variable air flow rates for different canopy sizes and foliage densities. Hence, the new sprayer was able to provide uniform air distributions along the tree heights inside canopies with different fan inlet diameters. A dimensionless parameter, which was the ratio of leaf area index and specific canopy depth to maximum canopy depth, was correlated with peak air velocity and dynamic airflow pressure.
In addition to the investigation of droplet sizes and air velocities for the new variable-rate sprayer, effects of modulation rate, fan inlet diameter and travel speed on spray coverage and deposition inside canopies were also determined. For a given condition, spray coverage increased as the modulation rate and fan inlet diameter increased. At a constant travel speed, variations in deposits inside canopies with the fan inlet diameter and modulation rate were insignificant. The coverage inside canopies increased as the travel speed decreased. The spray coverage inside canopies decreased as the canopy depth increased due to slow air disbursed inside dense canopies. The spray deposition and coverage inside canopies increased with the peak air velocity and dynamic airflow pressure as logarithmic functions increased.
风送式变量喷雾机能够在一定程度上解决传统的风送式喷雾机所存在的问题,能够根据靶标的具体结构参数调整药液的喷施量,变量喷施农药,从而实现有的放矢。未来变量喷雾机械的发展方向应是根据靶标的实际情况对辅助风速和药液喷施量同时实施变量控制。
本研究基于USDA-ARS-ATRU(美国农业部农业工程应用技术国家实验室)自主研发的新型五指风送式变量喷雾机。该喷雾机采用的五指风送式喷头将传统大的气流出口变成若干个小的圆柱形气流出口,可以提高雾滴的穿透性,改善气流在树叶密度较大的果树冠层内部的分布情况。该喷雾机对每个喷头药液输送端都采用PWM控制电磁阀的通断时间,单独控制每个喷头的药液流量。由于果树冠层各截面具体的结构特征参数显著不同,该喷雾机喷头的特殊结构对于果树每个区域的精密喷雾具有潜在的优势。目前该喷雾机已经实现了对靶标的有无、密度和大小变量喷施药液,然而,根据靶标的具体情况进行风速变量控制尚未实现。本研究采用调节风机进口内径以改变喷头出口风速的方法,探索根据靶标具体结构特征参数实现风速变量控制的可行性,为风送式变量喷雾机实施变量风速控制提供依据。
利用PWM控制电磁阀通断时间从而控制各个喷头药液流量的五指风送式喷头能够在变量工作条件下确保一致的雾滴粒径分布,这是实现根据靶标具体参数进行变量喷雾的前提条件。影响雾滴粒径大小的可控参数主要有电磁阀占空比、喷雾压力、喷头出口风速和喷雾药液物理特性。因此需首先研究该五指风送式喷头在这些相关变量参数影响下雾滴粒径的分布情况。雾滴粒径随着喷头出口气流速度、喷雾压力、喷雾药液特性的变化而变化。试验结果表明：在这四个变量中,喷雾压力对雾滴粒径大小的影响最大,其次是喷雾药液的物理特性,最后是喷头出口风速。对于给定的工作条件,当占空比为20%-100%时,雾滴粒径分布无显著变化,占空比为10%时,雾滴粒径分布波动较大,电磁阀占空比的切换频率是10Hz。为减少雾滴粒径在变量工作条件下有较大的波动,因此该喷雾机选择的工作条件是：保持喷雾压力恒定,占空比的工作范围为20%～100%。虽然风速对雾滴粒径的变化会有一定影响,但雾滴粒径在风速作用下的波动范围满足喷雾机变量作业要求。
为了检测该风送式变量喷雾机喷头出口气流的分布情况,通过调节风机进口内径(0.13m,0.15m,0.18m,0.34m)以改变喷头出口风速,并在不同行驶速度(0km/s,3.2km/h,4.8km/h,6.4km/h,8.0km/h)时,采用CTA风速测量仪检验该喷雾机在距离喷头出口不同远处(0.025m～3m)以及距离地面不同高度(0.2m～2m)处气流速度和动态气流压力的分布。喷头喷出气流在距离喷头出口0.027m处以500的扩张角喷射到空气中,距离喷头出口0.08m处单个五指风送式喷头相邻两喷口喷出气流开始混合。当喷雾机行驶速度为0km/h时,喷头出口气流速度随着风机进口内径的增大而增大,随着喷头出口距离的增大而按照双曲线函数关系递减。当喷雾机的行驶速度为3.2km/h～8.0km/h时,气流速度随着喷头出口距离的增大而减小,而动态气流压力在距离喷头出口(0～3m)范围内随着喷头出口距离的增大而缓慢增加。气流速度和动态气流压力随着风机进口内径的增大而增大。根据试验结果得知,通过改变风机的进口内径能够有效的改变喷头出口气流分布,并能够实现在给定的风机进口内径、给定的喷头出口距离所在的高度方向上气流分布均匀,表明了该喷雾机通过调节风机进口内径实现变量风速控制的可行性。当喷雾机行驶速度为3.2～8.0km/h,喷雾机行驶速度的变化对喷头出口气流速度和动态气流压力的分布无显著的影响。
在此基础上研究了该喷雾机在不同风机进口内径条件下,以一定的行驶速度经过果树时,喷头不同出口气流在果树树冠不同位置的分布情况。采用CTA风速测量仪,将传感器放置在冠层内部不同位置处,当喷雾机通过果树时,放置在冠层内部检测气流流速的传感器探测到气流分布呈脉冲形状。气流速度和动态气流压力随着冠层深度的增加而减少,且动态气流压力减少的幅度不如气流速度减少的幅度大。沿着高度方向(高、中、低)和喷雾机行驶方向(前、中、后)测量点的平均气流速度和平均动态气流压力分布基本保持一致。由此可以得知：该喷雾机沿着高度方向和喷雾机行驶方向在不同风机进口内径条件下,距离喷头出口相同远处冠层各区域内的气流分布一致。根据叶面积指数、树冠冠幅尺寸以及树冠内靶标的具体位置这三个参数组成的无量纲参数,建立了气流流速、动态气流压力与无量纲参数之间的指数关系。
实现变量喷雾的目的在于改善喷雾效果、提高喷雾效率、减少药液流失。为此研究了该喷雾机在不同占空比(20%-100%)、喷雾机行驶速度(3.2km/h,4.8km/h,6.4km/h)和风机进口内径(0.13m,0.18m,0.34m)等变量参数共同作用下,其在果树冠层内喷雾药液覆盖率以及沉降量的分布情况。对于给定的工作条件,冠层内喷雾覆盖率和药液沉积量随着风机进口内径和占空比的增大而增大,但是树叶密度和树冠外形尺寸也是影响喷雾覆盖率和药液沉积量的重要因素。随着喷雾机行驶速度的增大,喷雾药液覆盖率减少。对于给定的工作条件,区域内采样点的喷雾覆盖率均值沿高度方向和喷雾机行驶方向有微小的变化,但喷雾结果满足喷雾要求。同时,分别建立了喷头出口气流速度和喷雾覆盖率以及动态气流压力和喷雾覆盖率之间的关系曲线,喷雾覆盖率随着气流速度和动态气流压力的增大按照对数关系式增大。
根据喷头出口气流速度、动态气流压力与无量纲参数(由叶面积指数、叶面积指数、树冠冠幅尺寸以及树冠内靶标的具体位置组成)的指数关系,以及喷头出口气流速度、动态气流压力与喷雾覆盖率之间的对数关系,可以实现根据果树的特征参数估测冠层内气流速度和动态气流压力,然后推算出靶标位置点的喷雾覆盖率,根据喷雾作业对覆盖率的要求,再校准适当的气流风速,为未来风送式变量喷雾机实现风速变量控制提供理论依据。
The use of conventional air-assisted sprayer to apply pesticides has ensured production of high-quality fruits and ornamental nursery crops and enhanced our living standard. However, conventional air-assisted sprayers discharge constant air flows that are independent of tree size and foliage density. The air velocity profiles of these sprayers cannot be altered to uniformly deliver droplets to different plant canopies. In many cases, the air velocities are either too high or too tow and consequently, crops are either over sprayed or under sprayed. Another problem with the fixed air velocity patterns are off-target losses to the air and ground.
Variable-rate air-assisted sprayers that match spray outputs to target needs may be the solution to those problems associated with conventional sprayers. Development of future variable-rate sprayers should include a variable capacity control of both liquid and air flows to match tree canopy structures.
The cross section and foliage density of a tree vary throughout its entirety during the growing season. To accommodate this variability and achieve spray delivery, spray outputs should be tailored to each targeted section. An automatic air-assisted sprayer that implements five-port air-assisted nozzles to perform variable-rate spray outputs may have the potential to achieve this objective. This nozzle was developed to improve spray penetration and air jet velocity distribution inside dense nursery crops by dividing conventional large air jets into five small jets. The USDA-ARS-ATRU has developed the experimental air-assisted five-port sprayer to achieve liquid variable rates on tree occurrence, structure and foliage density. However, the mechanics to achieve variable air rates for this type of sprayer have not been developed. Also, to elucidate the mechanistic principles underlying air-assisted five-port nozzles in variable-rate applications, the magnitude of influence of the spray parameters on droplet size distributions first must be determined. Therefore, the objectives of this study were to investigate possible methods to achieve variable-rate air flow rates for this sprayer and to determine the effect of spray parameters and variable-rate air velocities on droplet size distributions. These objectives were used to form a basis for the future development of an automatic device to control air flow rates for variable-rate sprayers.
Design of the PWM-controlled, air-assisted, five-port nozzle with consistent droplet size distributions is the first step for the development of intelligent sprayers that have automatic variable spray output functions to match the variations in plant canopy structures. Parameters that influence droplet sizes from the nozzle include solenoid valve modulation rate, liquid pressure, air velocity discharged from the nozzle, and spray solution physical property. The effect of modulation rate, spray solution, air velocity, and liquid pressure on droplet size distributions produced from an air-assisted, five-port nozzle coupled with PWM solenoid valves were investigated. Droplet diameter consistencies varied with air velocity, liquid pressure, modulation rate, and spray solution physical properties. Among these four variables, droplet size was most affected by liquid pressure, followed by spray solution and then air velocity. Droplet diameters did not vary with modulation rates at20%～100%, but they were more variable at the10%modulation rate. The optimal conditions that minimize droplet diameter variations for variable-rate spray applications with the air-assisted five-port nozzle were to maintain a constant liquid pressure and to use modulation rate of20%～100%. However, droplet diameters also varied with air velocity, and this variation was accepted for the use of the air-assisted five-port nozzle in future automatic variable-rate sprayer development.
Unimpeded air jet velocities from the air assisted, five-port sprayer in an open field were measured at four heights above ground, seven distances up to3m from the sprayer outlets, and five sprayer travel speeds from0to8.0km/h. Air jet velocities were adjusted by changing the sprayer fan inlet diameter. Air velocities were measured with a constant temperature anemometer system coupled with hot-wire sensors. The air jets expanded at a50°angle and intersected with adjacent air jets at0.027m from the five-port nozzle. At a sprayer travel speed of0km/h, axial air velocities from nozzle outlets increased as fan inlet diameters increased and decreased as a hyperbola function as the distance increased. Variations in the peak air velocities and dynamic airflow pressures with the travel speeds of3.2to8.0km/h and heights of0.2to2.0m were insignificant. When the sprayer was in motion, own to air entrainment and air jet disturbance, the peak air velocities decreased and dynamic airflow pressures increased slightly as the distances from nozzle outlets increased. For all the parameters tested, the peak air velocities and dynamic airflow pressure decreased as the fan inlet diameters increased, demonstrating that changing fan inlet diameters achieved variable air flow rates with uniform air profiles.
Based on the conclusions of the air velocity distributions in an open field, this research was continued to determine whether variable air velocity distributions inside different sizes of tree canopies could be achieved by varying fan inlet diameters. Air jet velocities impeded by plant canopies were measured at various locations inside canopies of three different tree sizes and foliage densities. Tree heights were1.65,2.35and3.0m, and leaf area indexes were13.4,2.5, and1.5, respectively. Air jet velocities were adjusted by changing the sprayer fan inlet diameters and measured with a constant temperature anemometer coupled with hot-wire sensors. Peak air velocity and dynamic airflow pressure decreased with foliage density and canopy depth. For the0.34m fan inlet diameter, dynamic airflow pressure ratio of front portion to back portion of the canopies was8.0,1.5and2.6for Tsuga canadensis, Ficus benjamina and Acer rubrum, respectively. Similarly, the front to back peak air velocity ratio was8.55,1.59, and1.89times for T. canadensis, F. benjamina and A. rubrum, respectively. Variations were significant for peak air velocities and dynamic airflow pressures among the three different tree volumes and foliage densities. Increased fan inlet diameters from0.13to0.34m, increased average airflow pressure from0.4to0.8N/m2,0.8to1.5N/m2, and0.5to0.9N/m2inside canopies of T. canadensis, F. benjamina and A. rubrum, respectively. Therefore, alterations of fan inlet diameters for the five-port air assisted sprayer achieved variable air flow rates for different canopy sizes and foliage densities. Hence, the new sprayer was able to provide uniform air distributions along the tree heights inside canopies with different fan inlet diameters. A dimensionless parameter, which was the ratio of leaf area index and specific canopy depth to maximum canopy depth, was correlated with peak air velocity and dynamic airflow pressure.
In addition to the investigation of droplet sizes and air velocities for the new variable-rate sprayer, effects of modulation rate, fan inlet diameter and travel speed on spray coverage and deposition inside canopies were also determined. For a given condition, spray coverage increased as the modulation rate and fan inlet diameter increased. At a constant travel speed, variations in deposits inside canopies with the fan inlet diameter and modulation rate were insignificant. The coverage inside canopies increased as the travel speed decreased. The spray coverage inside canopies decreased as the canopy depth increased due to slow air disbursed inside dense canopies. The spray deposition and coverage inside canopies increased with the peak air velocity and dynamic airflow pressure as logarithmic functions increased.
引文
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[1]Fox, R. D., R. C. Derksen, H. Zhu, R. D. Brazee and S. A. Svensson. (2008). A history of air-blast sprayer development and future prospects [J]. Transactions of the ASABE 51 (2):405-410.
[2]Abramovich, G. N. (1963). The theory of turbulent jets [M]. The M.I.T. Press, Cambridge, MA. 671pp.
[3]Brazee, R. D., R. D. Fox, D. L. Reichard and F. R. Hall. (1981). Turbulent jet theory applied to air sprayers [J]. Transactions of the ASABE 24 (2):266-272.
[4]Zhu, H., R. D. Brazee, R. C. Derksen, R D. Fox, C. R Krause, H. E. Ozkan and K Losely. (2006) Aspecially designed air-assisted sprayer to improve spray penetration and air jet velocity distribution inside dense nursery crops [J]. Transactions of the ASABE 49 (5):1285-1294.
[1]Brazee, R. D., R. D. Fox, D. L. Reichard and F. R. Hall. (1981) Turbulent jet theory applied to air sprayers [J]. Transaction of ASAE 24 (2):266-272.
[2]Fox, R. D., R. D. Brazee and D. L. Reichard. (1985) A model study of the effect of wind on air sprayer [J]. Transaction of ASAE 28 (1):83-88.
[3]Fox, R. D., R. D. Brazee, S. A Svensson and D. L. Reichard. (1992) Air jet velocities from a cross-flow fan sprayer [J]. Transaction of the ASAE 35 (5):1381-1384.
[4]Reichard, D. L., R. D. Fox, R. D. Brazee and F. R. Hall. (1979) Air velocities delivered by orchard sprayers [J]. Transaction of ASAE 21 (1):69-74,80.
[5]Svensson, S. A., R. D. Fox and P. A Hansson. (2002) Forces on apple trees sprayed with a cross-flow fan air jet [J]. Transaction of ASAE 45(4):889-895.
[6]Svensson, S. A, R. D. Brazee, R. D. Fox and K. A Williams. (2003) Air jet velocities in and beyond apple trees from a two-fan cross-flow sprayer [J]. Transaction of ASAE 46 (3):611-621.
[7]Zhu, H., R. D. Brazee, R. C. Derksen, R. D. Fox, C. R. Krause, H. E. Ozkan and K. Losely. (2006) A specially designed air-assisted sprayer to improve spray penetration and air jet velocity distribution inside dense nursery crops [J]. Transaction ofASABE 49 (5):1285-1294.