低压滴灌系统文丘里施肥器的结构参数优化及变量施肥调控方法

Low-pressure drip irrigation not only has very high utilization rate of water and fertilizer, but also can reduce the irrigation system’s construction cost and operation cost. Venturi injector is highly valued in facility agriculture and the cultivation of fruit trees as a kind of commonly used fertigation equipment, because of low cost, simple structure and without external power, but there are still many of the technical issues needed to be improved urgently in the application process. According to the existing Venturi injectors’ current status that requiring relatively high inlet pressure, being difficult to regulate fertilization concentration and the fertilization concentration easy to be affected by fluctuation of inlet pressure of the main pipe, and aiming at low-pressure drip irrigation systems, the project focuses on the study of structural parameter optimization and regulating method of variable rate fertilization for the Venturi injector with a series of inlet pressures and specifications of the parallel main pipe, within the pressure range of low-pressure drip irrigation systems. The aim of the study is to explore the best combination of main structural parameters and the best adjusting method for variable rate fertilization of the Venturi injector which has to be suitable for low-pressure drip irrigation systems, and to construct a corresponding electric control adjusting equipment and its regulating model for variable rate fertilization, by using the method of combining numerical simulation and experimental verification, with the target of improving fertilization performance and broadening the scope of fertilizer concentration which has to be continuously adjustable. Therefore, the study will realize the innovation of a kind of automatic regulating method for variable rate fertilization of Venturi injectors, and a new way will be opened up for precise management of water and fertilizer in low-pressure drip irrigation, and the results of the study have important practical significance for precision agriculture and efficient fertilization.

低压滴灌不仅水肥利用率高，还可以降低灌溉系统的建设成本和运行成本。文丘里施肥器因成本低、结构简单、无需外部动力等优点，作为一种常用灌溉施肥装置在设施农业和果树栽培中受到高度重视，但在应用过程中还存在许多急需改进的技术问题。本项目针对现有文丘里施肥器压力损失大、施肥浓度难以调节且受主管水压波动影响的现状，面向低压滴灌系统，重点研究低压滴灌压力范围内，不同进口压力及各种常用规格的并联主管下，文丘里施肥器的结构参数优化设计及变量施肥的调控方法，以提高吸肥性能和拓宽施肥浓度连续可调的范围为目标，采用数值模拟计算与试验验证相结合的方法，探寻适合于低压滴灌的文丘里施肥器主要结构参数的最佳组合及其变量施肥的最佳调节方式，研究相应的电控调节装置并构建其变量施肥调控模型，这将会实现文丘里施肥器变量施肥自动调控方法的创新，为低压滴灌系统的水肥精细管理开辟一条新途径，对精准农业和高效施肥具有重要的现实意义。

文丘里施肥器因成本低、结构简单、无需外部动力等优点，作为一种常用灌溉施肥装置广泛应用于设施农业中，但在实际应用中还存在压力损失大、施肥浓度难以调节且受主管水压波动影响等急需改进的技术问题。本项目针对上述不足，以提高吸肥性能和拓宽施肥浓度连续可调的范围为目标，面向低压滴灌系统，研究低压滴灌压力范围内，文丘里施肥器的结构参数优化设计及变量施肥调控方法。主要研究结果如下：1）采用CFD数值模拟分析与试验相结合的方法，对DN25、DN32、DN40、DN50和DN65 5种规格文丘里施肥器进行了结构优化设计，得出最佳结构参数为a=b=25 mm、A=a1=6.25 mm、B=C=20 mm、λ=0.25、α=25°、β=8°、γ=135°、θ=1.5，试验结果表明临界吸肥进口水压均小于0.009MPa，且当进口水压为0.05MPa时吸肥浓度分别为9.30%、9.08%、8.07%、8.04%、5.97%（大于一般农作物施肥浓度），能在工程上满足低压灌溉施肥要求；2）为进一步降低对进口水压的要求，设计了一种双吸肥口文丘里施肥器，确定了最佳结构参数为比λ=0.3、α=20°、β=8°、θ=1.1，试验结果表明临界进口压力为0.007 MPa，且当进口压力为0.05 MPa 时吸肥浓度达13.6%，与现有文丘里施肥器相比，在获得同等或更高的吸肥性能时具有更低的工作水压，更适用于低压滴灌系统；3）分别在文丘里施肥器的入口、出口和吸肥口开展了吸肥浓度调控试验，结果表明在低压滴灌压力范围内，通过调节文丘里施肥器吸肥管流量进行变量施肥的调控效果最佳；4）以针型阀为执行部件，研制了文丘里施肥器变量施肥的电控调节装置，采用模糊控制与PWM变速调节相结合的方法，建立了变量施肥调控模型，试验结果表明其最大施肥浓度误差为0.16%，响应时间为5.3~8.5 s，能满足实际应用要求；5）研制了一种大量元素水溶肥种类快速识别装置、同心圆柱环型电容式肥液浓度在线检测传感器和一体化可调式恒压供水试验装置。本项目扩充了文丘里施肥器变量施肥的理论与方法，拓宽了文丘里施肥器的应用范围，为低压滴灌系统水肥精细管理开辟一条新途径，对精准农业和高效施肥具有重要理论价值和现实意义。