An improved finite element model for the hydraulic analysis of drip irrigation subunits considering local emitter head loss

Abstract

A good hydraulic design of drip irrigation systems requires an accurate evaluation of the friction head loss that occurs in pipes as well as the local head loss induced by the presence of emitters. Previous approaches on theoretical design usually neglect the local emitter head loss or consider it equal to the friction loss produced by an equivalent length of the straight pipe, which may lead to substantial errors. In this study, an improved finite element-based formulation is presented for the hydraulic analysis of drip irrigation subunits. Local head loss is calculated as a fraction of the kinetic head using the results from recent experimental studies on on-line and integrated in-line emitters (Method 1), or by the equivalent length (Method 2). A custom Matlab software script was developed and the two methods are compared for accuracy and convergence speed. For practical purposes, the head loss components along lateral direction are analyzed for two types of in-line emitters and a manifold design example is also provided. Acquired data indicate that considering an equivalent length as a constant value leads to a higher percent error between the numerical solution and the experimental data. The percentage of local head loss to the total head loss varies dramatically from 6.3 to 49.2% and this result is in good agreement with the results from alternative procedures available in the literature. The decrease in the local head loss coefficient allows a slight increase in manifold length. In general, the finite element model with solution method 1 can be a fast, accurate, and convenient way of designing a drip irrigation pipe network system.