微喷带喷孔水量分布模型构建

喷孔水量分布是影响微喷带喷洒均匀性的重要的喷洒特性。该研究旨在考虑水分分布构建一种有效的水量分布模型。研究选取一种常用微喷带，开展喷孔水量分布试验，考虑其单峰和双峰分布特征，建立了二维正态分布模型，明确了模型参数的物理意义，分析了压力、喷射角度、喷孔面积对模型参数的影响。结果表明，该模型能较好地拟合试验中微喷带喷孔的单峰和双峰水量分布，拟合峰值与试验峰值相对误差小于15%，决定系数高于0.80。研究还发现，压力对单峰峰值的影响较小，主要改变了双峰分布中垂直微喷带方向的峰值位置和喷洒水量分布范围。随着喷射角度增大，喷孔的喷洒区域向喷孔方向靠近，在压力为69.0 kPa时，单峰峰值在喷射角度约57.5°时开始递增，垂直微喷带方向的喷洒水量分布范围越来越集中。喷孔的喷洒区域和喷洒水量分布范围随着喷孔面积的增大逐渐增大，较小的喷射角度和较大的喷孔面积使喷孔的水量分布更复杂。研究提出的喷孔水量分布的单双峰二维分布模型，可为微喷带的研制和喷孔的优化加工提供理论参考。

Development of water distribution model of single orifice on micro-sprinkling hose

Abstract: Micro-sprinkling hoses have been widely applied in water-saving irrigation equipment, due to their easy reliable installation, strong anti-clogging capability, and low cost. The performance of micro-sprinkling hoses can depend mainly on a set of orifices. Particularly, the water distribution of a single orifice can pose a significant impact on the spraying uniformity. Previous studies were focused on the spray characteristics of a single orifice on the surface with range, wet area, and width of the drying zone. But it was difficult to quantitatively analyze the spatial characteristics of water distribution. Therefore, it is necessary to accurately determine the water distribution of a single orifice in a micro-sprinkling hose. In this study, an indoor experiment was carried out for the water distribution of the micro-sprinkling hoses without the wind effect. 12 holes were set in the belt with a folded inner diameter of 54 mm, and a wall thickness of 0.5 mm. Specifically, the measured orifice area of the micro-sprinkling hose was 0.073-0.279 mm2, the orifice spacing was 47-52 mm, and the hole spacing was 47-52 mm. Among them, the indoor temperature was about 20℃, and the relative humidity was about 55%. A pressure regulator was selected for the fluctuated pressure of the micro-sprinkling hose caused by the municipal water supply. The length of the sample hose was 2 m in the test. The spraying angle varied from 40° to 90°, and the working pressures were 41.0, 69.0, and 103.0 kPa. The micro-sprinkling hose was laid flat on the spray side of rain gauges. The origin of the coordinate system was placed at the center of the single orifice, where the direction of flowing water in the micro-sprinkling hose was set x-axis, and the placement direction of rain gauges was set y-axis. The indoor test indicated that there was a unimodal or bimodal two-dimensional water distribution of a single orifice. Unimodal and bimodal distribution models were developed to fit the water distribution using the normal distribution probability density function. The results showed that the peak error was small between the fitting and experimental value, and the coefficient of determinations was greater than 0.80, indicating an excellent agreement with the experimental measurements. A systematic analysis was also made to explore the impacts of pressure, spraying angle, and orifice area on the coefficients in both unimodal and bimodal distribution models. Consequently, there was a little effect of pressure on the peak value of intensity distribution during water application, but the higher peak value and the range of irrigated area were found in the spraying direction of bimodal distribution. Furthermore, the irrigated area was reduced to intensify the application rate, as the spraying angle increased. Once the spraying angle reached a critical value, the peak value started to increase, particularly for the more concentrated distribution of irrigation intensity in the spraying direction. Therefore, the larger orifice areas resulted in the larger irrigated areas. The finding can provide an important reference for the design and optimization of micro-spray hoses for water-saving irrigation.