为解决固定式旋转喷头低压喷灌时，水射流向末端集中形成水量分布不均匀的问题，提出水气两相射流进行喷灌的方法。在摇臂喷头结构的基础上，增加掺气结构，形成掺气射流喷头，以相同工作水压力、射流仰角、喷嘴出口流量相同为约束，以及不考虑副喷嘴对喷洒的影响，对比了掺气与不掺气2种情况下 PY20喷头的射程、径向水量分布、1倍射程间距的正方形组合喷灌均匀系数，雨滴粒径等参数。试验结果表明：原不掺气摇臂喷头出口直径7 mm，安装内径2 mm 的掺气管后出口直径改为8.3 mm，此时两者具有相同的出口流量，2种喷头在相同工作压力下具有近似相等的射程；在掺气喷头工作水压低至100 kPa 情况下，喷头仍具有76 mm 水银柱高差的掺气负压能力；掺气摇臂喷头改善了径向水量分布线射程中段的水量，使水量分布线发生了中段略微增高、末端略下降的变化，从而使1倍间距的正方形组合喷灌均匀系数在低于国家标准工作压力的200 kPa 情况下，从62.8%提高到68.8%；采用激光雨滴谱仪测量射程中部和末端2个地方的水滴粒径表明：掺气状态下射程中部的水量累积百分比中位直径 d50远大于不掺气状态，射流末端对比 d50则小于不掺气状态，说明掺气改变了喷头的雨滴粒径分布。该文试验结果证明掺气摇臂喷头在农业喷灌中应用具有可行性。%Research on sprinkler irrigation is developing toward the low pressure spray. When the fixed rotary sprinkler works at the low pressure, there is too much water concentrating at the end of jet, causing seriously uneven water distribution. In order to solve this sprinkler irrigation problem, an aeration jet method is put forward in this paper. Based on the structures of impact sprinkler PY20, a gas suction component is adopted to form an aeration impact sprinkler. The axis of gas suction pipe coincides with the axis of sprinkler tube. The environmental gas is sucked into the impact sprinkler due to the negative pressure formed by jet flow. Performances of PY20 impact sprinkler with and without aeration were compared under the same conditions of working pressure, trajectory angle, flow rate of the sprinkler, and the effect of sub-nozzle has not been taken into account. . The comparison parameters include the ranges of jet, water distribution curves along the radial direction, coefficients of distribution uniformity for square combination with spacing factor equal 1, droplet size distribution and so on. The experiment finds that the outlet diameter of original impact sprinkler is 7 mm; when 2 mm inner diameter gas pipe is installed, the outlet diameter should be changed to 8.3 mm for the aeration impact sprinkler to keep the same flow rate with the original impact sprinkler. Two types of sprinklers nearly have the same jet range under the same working pressure. The negative pressure of gas pipe is measured by U-gauge, and the height difference of mercury column increases with the impact sprinkler working pressure, which means that the intake capacity becomes stronger as the working pressure increases. As the working pressure reduces to 100 kPa, the aeration sprinkler still has the ability of gas suction and it has 76 mm height of mercury column. The aeration method improves the water distribution curve at the middle jet range, and it makes water distribution line a litter higher at the middle jet range, while a little lower at the end of jet range. In order to compare the aeration impact sprinkler with original impact sprinkler when they are used in combination sprinkler irrigation, and to make sure whether the aeration method can improve the uniformity of water distribution or not, the square combination with spacing factor equal 1 is selected to do a test. For the combined 4 sprinklers, its radial direction water distribution curve is overlapped through linear interpolation. At the working pressure of 200 kPa which is lower than national standard, the coefficient of distribution uniformity (CDU) is enhanced from 62.8% to 68.8% by the aeration method. Experiments are also done by using laser raindrop spectrometer. The raindrop size distribution produced by aeration impact sprinkler and original impact sprinkler is compared at the location of jet end and at the middle of jet range. At the middle jet range, the aeration impact sprinkler has a much larger median diameter of water accumulation frequency than impact sprinkler, while it has the smaller diameter at the end of jet range. It can be proved that the gas sucked into the jets changes the spray droplet size distribution. The experimental results in this paper prove that the aeration impact sprinkler is feasible for applying to agricultural irrigation. There are many further investigations which need to do, such as how the aeration sprinkler performance changes with the gas flow rate, and the lowest working pressure and the optimized structure for aeration sprinkler need to be studied.
展开▼
