Abstract
Aim of study: To investigate how the cross section of a drip-irrigation tape affects local head loss.Area of study: The work was carried out in the laboratory of Irrigation hydraulics, College of Water Conservancy and Environment, Three Gorges University, Yichang, Hubei province.Material and methods: Tapes with six different wall thicknesses were studied experimentally to determine the relationship between cross-section deformation, wall thickness, and pressure. Based on the experimental results, we determined the factors that influence local head loss in drip-irrigation tapes by numerical simulation and dimensional analysis.Main results: The cross-sectional shape of the drip-irrigation tape varied with pressure: under low pressure, the cross section was nearly elliptical. The cross-sectional shape of the tape strongly influenced the local head loss, which was inversely proportional to the 0.867th power of the flattening coefficient of the drip irrigation tape. We expressed the local head loss of a drip-irrigation tape equipped with integrated in-line emitters by considering the deformation of the cross section. Under the conditions used in this study, when the cross section is circular, the ratio of local head loss to frictional head loss was about 10% but, when the cross section is elliptical, this ratio increased to 15%.Research highlights: The shape of the cross section of a drip-irrigation tape is nearly elliptical under low pressure. Local head loss is inversely proportional to the 0.867th power of that is the flatting coefficient of the drip-irrigation tape. Local head loss is about 1.5 times for elliptical tape than circular tape.
Highlights
In the field of micro-irrigation, the widely used technique of low-pressure drip irrigation is highly efficient and saves energy
Under the conditions used in this study, when the cross section is circular, the ratio of local head loss to frictional head loss was about 10% but, when the cross section is elliptical, this ratio increased to 15%
When transporting water at low pressure, the cross section of these tapes is often noncircular, and this deformation can affect the resistance to water flow
Summary
In the field of micro-irrigation, the widely used technique of low-pressure drip irrigation is highly efficient and saves energy. The study of head loss in drip-irrigation tapes generally assumes a fixed circular lateral cross section, without considering how modifications to this shape affect head loss (Neto et al, 2009) Exceptions to this trend include the work of Neto et al (2014) and Provenzano et al (2016), who studied the frictional head loss of soft, round, polyethylene pipe and considered how, when transporting water under high pressure, the cross section of the pipe affects the frictional head loss. One approach to the problem consists of numerical and dimensional analyses, which are widely used to study pipeline hydraulics (Demir et al, 2007; Provenzano et al, 2007; Yildirim, 2010; Wang et al, 2018) These two methods are used to study the local head loss of drip-irrigation tapes with varying cross section. The data were divided into two groups: one group was used to verify the numerical simulation, and the other group was used to verify the analytical analysis (see below)
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