摇臂式喷头与全射流喷头水滴分布对比试验

摇臂式喷头(impact sprinkler,PY)出口流体为单相水,全射流喷头(complete fluidic sprinkler,PXH)出口流体为气液两相流,为了深入探索2种类型喷头水滴分布的存在规律及差别,该文采用激光雨滴谱仪测量技术对PY及PXH喷头的水滴分布进行试验研究,采用体积加权法分析了这2种喷头在工作压力为150、200、250、300和350 k Pa情况下,距喷头不同距离处的水滴频率分布、水滴累计频率及中数直径的变化规律。结果表明:1)PXH喷头水滴频率普遍小于PY喷头。PXH喷头和PY喷头水滴频率分布分别符合对数正态分布和正态分布;2)PXH喷头水滴累计频率变化更加均匀,2种喷头的水滴直径分布均符合指数函数分布规律,在距离喷头距离较小时,PXH喷头比PY喷头的拟合精度更高,在距喷头距离为4 m下,PXH喷头拟合函数的R2值较PY喷头高3.5%;3)在低压条件下距喷头不同距离时,PXH喷头的水滴分布更加连续及均匀。建立了2种喷头中数直径与工作压力及距喷头距离的函数。该结果完善了多类型喷头喷洒水力学特性,对研究射流运动模型及喷洒的外特性提供了参考。

Comparison of droplet size distribution experiments between complete fluidic sprinkler and impact sprinkler

Abstract: Sprinkler is the key equipment of sprinkler irrigation system. The hydraulic performance of sprinkler is directly influenced by the quality and efficiency of irrigation. The fluid at the impact sprinkler (PY) outlet is single-phase water, and that at the complete fluidic sprinkler (PXH) outlet is gas-liquid two-phase flow. In order to explore the distribution regularity and difference of the 2 types of sprinkler droplets, based on the laser raindrop spectrometer measuring technique (laser precipitation monitor, LPM), the experimental study on droplet size distribution of PY and PXH sprinkler was carried out, and the volume weighted method was used to analyze the water droplets frequency distribution, cumulative frequency and medium diameter variation at different distances from sprinklers. The working pressures were 150, 200, 250, 300 and 350 kPa, respectively. The results showed that the droplets frequency of the PXH sprinkler was generally less than the PY sprinkler, and the droplet distribution range of PXH sprinkler was wider than the PY sprinkler under different pressures. Under the low pressure conditions, the droplet distribution of PXH sprinkler was more continuous and uniform. The droplets frequency distribution of PXH and PY sprinkler conformed to logarithmic normal distribution and normal distribution respectively. With the distance from the sprinkler increasing, the slope of the droplet cumulative frequency curve decreased gradually. With the working pressure increasing, the slope of the droplet cumulative frequency curve at different distance from the sprinkler decreased gradually, and the droplet cumulative frequency variation for the PXH sprinkler was more uniform. The droplet cumulative frequency distribution of the 2 kinds of sprinklers conformed to the index function distribution, and when the distance from sprinkler was short, the fitting accuracy of the PXH sprinkler was higher than the PY sprinkler. At the distance of 2 and 4 m from the sprinkler, the correlation coefficients of the fitting function of the PXH sprinkler were respectively 0.9% and 3.5% higher than the PY sprinkler. At the distance of 6 and 8 m from the sprinkler, the correlation coefficients of fitting function of the PY sprinkler were respectively 3.3% and 1.2% higher than the PXH sprinkler. The median diameter increased with the distance from the sprinkler, and the median diameter decreased with the increasing of the working pressure. Under the same working pressure, with the distance from the sprinkler increasing, the increase percentage of the droplet median diameter for the PXH and PY sprinkler gradually became larger. Under the same pressure and the same position, the droplet median diameter of the PY sprinkler was less than the PXH sprinkler. The function of the relationship between median diameter, working pressure and distance from the sprinkler was established. Under the condition of 150 kPa and 7 m far from the sprinkler, the median diameter of PXH sprinkler was 66.2% higher than the PY sprinkler. Under the condition of low pressure, the droplet size distribution of the PXH sprinkler was more continuous and uniform at different distances from the nozzle, which was conducive to water crops and make the force uniformly distributed. The results provide the reference for the study of the jet motion model and the external spraying characteristics.