Temperature and sediment effects on the hydraulics of drip irrigation lines

Abstract

Experiments were conducted with 180 m long T-tape and Agrifim emitter lateral lines in the laboratory and field to determine the effects of water temperature and sediment concentration on the hydraulics of drip irrigation laterals. The flow regime was laminar through the T-tape emitter and turbulent through the Agrifim emitter. Water temperature decreased along the lateral line in the laboratory where the inlet water temperature was higher than ambient air. In contrast, temperatures increased along a lateral line exposed to the sun in the field with an inlet temperature lower or slightly higher than that of air. The rate of increase or decrease was more pronounced towards the end of the line. The effect of temperature was highly significant on emitter flow rates obtained for a T-tape emitter as opposed to those recorded for the Agrifim emitter in the laboratory; however, the increase of emitter flow rates due to temperature was reduced by plugging in the field. Discharges of T-tape emitters were dominated by the hydraulic pressure for the first half of the line with the water temperature being more important for the second half of the line in both the laboratory and field. Measured discharges of Agrifim emitters were dominated by the hydraulic pressure for the entire lateral length especially in the laboratory. The Darcy-Weisbach friction factor, as opposed to the Blasius friction factor, is recommended for design because it accounts for the wall roughness of the pipe. The Hazen-Williams roughness coefficient was related to Reynolds number to improve the drip system design. Total friction losses, as a result of water viscosity changes and lateral discharge variations due to temperature, increased significantly for the T-tape emitter lateral in the laboratory and field for different inlet water temperatures and inlet-outlet temperature variations. In contrast, total friction losses decreased for the Agrifim emitter lateral primarily because of water viscosity changes with temperature. The sediment concentration along an Agrifim emitter lateral in the laboratory decreased sharply in the second half of the line when the flow velocity dropped below 0.29 ms⁻¹ . Also friction losses increased for an Agrifim emitter lateral in the laboratory as the inlet concentration increased from 200 to 650 mg/l.