Applying hypothesis of self-similarity for flow-resistance law of small-diameter plastic pipes

In this paper the writer reports the results of an investigation carried out to test the applicability of the self-similarity hypothesis for determining the flow-resistance law in small-diameter plastic pipes. The incomplete self-similarity (ISS) hypothesis is applied for establishing both the flow-resistance law and the velocity distribution. The analysis shows that the head loss per unit length can be accurately estimated using a theoretical approach based on the ISS hypothesis for the velocity profile in a circular smooth pipe. A new relationship between the Gamma coefficient of the power-velocity profile and the flow Reynolds number, based on previous measurements carried out in plastic polyethylene (PE) pipes with nominal diameter equal to 16, 20, and 25 mm and for flow Reynolds numbers ranging from 3,037 to 36,112, is also established.