Hydraulics of Microtube Emitters

Laboratory experiments show that the Darcy-Weisbach equation for hydraulically smooth pipe can be used to determine friction drop for microtubes with a diameter ranging from 0.8 mm to 4 mm. It can be concluded that the smooth pipe equation (using Blasius friction equation) can be used with reasonable accuracy for all sizes of drip irrigation tubes in turbulent flow conditions. A computer numerical solution was applied to separate minor loss from the total pressure drop; a minor loss equation was developed for microtube for combined flow, transition zone and turbulent conditions. The minor loss for laminar flow condition is small and can be neglected. For flow in the transition zone and turbulent flow the minor loss coefficient was determined to be 2.32 and 1.69 respectively. A better correlation was obtained between the friction coefficient f and Reynolds number when the minor loss was separated. It shows the microtube is slightly smoother than the hydraulically smooth tube as specified in the Moody diagram.