Document Type : Article
Authors
1
Department of Irrigation and Drainage Engineering, Aburihan College, University of Tehran, Tehran, Iran
2
Associate Professor, Agricultural Engineering Research Institute, Ministry of Agriculture – Jahad, Karaj, Iran.
3
Professor, Department of Renewable Energies and Environmental Engineering, University of Tehran, Tehran, Iran.
4
Postdoc Associate, Rice University, Houston, Texas, United States
5
Department of Irrigation and Reclamation, Faculty of Agriculture, University of Tehran, Karaj, Iran.
10.24200/j30.2024.62619.3234
Abstract
In designing of drip irrigation systems, Hazen-William’s equation is usually used to determine the hydraulic head loss. The mentioned equation is suggested for pipes with diameters greater than 75 mm and flow rates above 2.3 l/s. However, for trickle irrigation lateral pipes with diameters from 16 to 32 mm are generally used. In this case, the calculated hydraulic head loss is lower than the actual hydraulic head loss, and subsequently, the hydraulic pressure at the desired point will be lower than the required value; In other words, the output flow from the droppers will be reduced and the uniformity of water distribution will be less than the expected amount. Herein, using laboratory models and the use of polyethylene pipes with a diameter of 16, 20, 25 and 32 mm, the amount of hydraulic loss was measured for different flow rates and according to the permissible velocity limits. Hydraulic pressures were measured using data Logger, one record for each second, and the discharge was adjusted volumetrically. To control the discharge and the hydraulic pressure, a by-pass pipe was installed on the physical model. The amount of hydraulic head loss was measured for different flow rates in the permissible flow velocity range (1-2 m/s). Then, by analyzing the recorded data, a new relationship was obtained that calculates the amount of hydraulic head loss in 16 to 32 mm pipes as a function of flow rate and pipe diameter. The Hazen-Williams equation was compared with the results of Moody, Churchill and Colebrook methods, as well as the actual measured values. According to the results, the largest error between the measured and the calculated head loss was for the Colebrook & White equation for the 25 mm pipe and the smallest error was for the same equation for the 32 mm pipe. The obtained relationship is recommended for polyethylene pipes with diameter of 16 to 32 mm and with Reynolds number above 2000 with high confidence. One of the advantages of the obtained relationship is its independence from the Hazen-Williams roughness coefficient and its remarkable accuracy.
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