Analysis of Geometrical Relationships and Friction Losses in Small-Diameter Lay-Flat Polyethylene Pipes

Abstract

19The use of lay-flat polyethylene pipes for microirrigation of horticultural crops has been 20 receiving a widespread attention in the last few decades. The industry has made significant 21 improvements in the hydraulic performance of lay-flat pipes, so that their use is still expected to 22 increase, mainly because of the enhanced competition for water worldwide, that imposes the use of 23 irrigation systems with potentially high application efficiencies and characterized by a limited 24 installation costs. for the three pipes to 0.11 mm, 0.19 mm and 0.10 mm, resulted higher than those obtained with the 37 photographic method, whose values resulted generally lower than 0.06 mm. At the same time, the 38 tests allowed to identify that most of the changes of the pipe dimensions occur in the range of 39 pressure from 0 kPa to about 30 kPa, being the dimensions quite similar at higher values, when the 40 pipes tend to assume a round cross section. When water pressures increase over a certain limit, p lim , 41 both vertical width and horizontal height still tend to rise, because of the pipe deformation due to 42 the elasticity of the material, with a trend that resulted more marked for the pipe with the lowest 43 thicknesses. According to the experimental data, the relationships between the pipe effective 44 diameter, to be used to evaluate pipe friction loss, and the water pressure, were then determined on 45 the three considered pipes. 46On the other side, based on measured friction losses and on pipe effective diameters, it was verified 47 that the relationship between the Darcy-Weisbach friction factor, f, and the Reynolds number, R, 48 can be still described with a power equation in which, by assuming a value of -0.25 for the 49 exponent, the coefficient resulted lower than the theoretical and equal to c=0.285. 50For the three investigated pipes the errors associated to estimated friction loss per unit pipe length 51 were finally evaluated by considering: i) the experimental relationships between friction factor and 52

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