微灌双向有坡毛管情况下支管位置的确定方法

在微灌支管两侧布置双向毛管,有节省投资、节能、提高灌水质量的优点。该文在有限孔数毛管水力学的基础上,对双向有坡毛管布置时的支管位置确定方法做了较为完整的讨论,包括:计算中会遇到的4种情况,汇总了计算中涉及的解析公式,提出了合理孔数试算公式和进口段长度计算公式,并提出了毛管进口段总损失扩大系数的改进算式。确定支管位置(即毛管长度)的基本条件是:在两侧毛管各灌水器流量的平均值均等于设计流量的前提下,使两侧毛管的进口水头相等。原则上应分两步来实现:第一步是根据所遇情况选择适用算式,以两侧毛管最大水头偏差最接近为条件,试算确定毛管的合理孔数;第二步是计算两侧毛管的上游首孔水头,然后得到二条毛管的进口段长度。如两侧毛管首孔水头极为接近,则可直接按两侧毛管进口段长度相等来处理。通过算例说明该方法可在微灌系统设计中应用,对喷灌系统的干管布置也有参考意义。

Method of determining locations of branch pipe on slope with paired capillaries in micro-irrigation system

Arrangement mode that both sides of the branch pipe of micro-irrigation system with paired capillaries has advantages of investment-saving, energy-saving and high quality of irrigation. Based on hydraulics with limited holes in capillary, methods of determining locations of branch pipe on slope with paired capillaries was discussed: four cases in calculations; the corresponding analytical formula; trial calculation of formula on reasonable holes; length of entrance region; improved formula of enlargement coefficient of total loss in entrance region of capillaries. The basic principle of determining locations of branch pipe or length of capillaries is the equality of entrance water head in paired capillaries on the basis of average discharge of emitters in paired capillaries equaling design discharge. Two steps should be followed: 1) choosing the proper algorithm and determining holes by trial calculation; 2) calculating water head of the first hole in upper reaches of paired capillaries and the corresponding length of entrance region. If two water head of the first hole are approximately equal, the corresponding entrance region could be considered as the same length. Numerical examples shows methods proposed in this paper can be applied in micro-irrigation system design and have references in main pipe arrangement of spray irrigation.