多孔变径出流管标准化管径设计方法

A design method for tapered multioutlet pipeline with nominal diameters

针对多孔出流同径管存在压强水头偏差大、造价高、流速分布不均匀的问题,通过对多孔出流管进行变径设计,可使每个孔口实际压强水头等于要求的压强水头,从而提高灌水均匀度.以管道成本最小为目标,以管道允许压强水头差为约束条件,利用微分法得到多孔出流管最优管径组合,初步确定管径范围;在此基础上,结合市场上可购买的商用管道,选择几种靠近初选管径的商用管道,进行管道标准化设计,不同管径的多口出流管压强水头坡度线切点处的斜率等于允许水力坡度,允许水力坡度由允许最大压强水头差和地面高差决定,从而确定出不同管径对应的水力坡度线的交点,进而分析出不同管径对应的管长.实例应用表明,利用该设计方法,每个孔口要求的压强水头与实际压强水头接近,由于管径随管道流量的减小而减小,不仅可以使管道内流速分布均匀而且可以降低造价,该方法计算简单方便,可以在Excel表格上完成,计算结果可直接用于多孔出流管的设计中.

The single-size multioutlet pipe had some disadvantages,such as big pressure head variation,high cost and difference of velocity from inlet to outlet of pipe.However,the multiple-size multioutlet pipe can solve above problems.A design method for the tapered multioutlet pipeline was proposed.Firstly,a series of optimal diameters were obtained based on Lagrange method and the diameters scopes of multioutlet pipeline were determined.Then,several commercially available pipe sizes that are very close to the diameter obtained in the first stage are selected.By using proposed formula,pipe lengths corresponding to nominal diameters are calculated.The pressure head variation of the pipe with different nominal pipe size can be equal to a desired pressure head variation.The cost of multiple-size pipe is lower than that of single-size pipe.Because the pipe size decreased with the decrease of pipe discharge,velocity distribution in pipe is uniformity.The cost was lower than that of single-size pipe.The design result can be used to engineering operation.