Hydraulic performance and energy dissipation effect of two-ways mixed flow emitter in drip irrigation

Abstract: The two-ways mixed flow emitter is a new kind of drip irrigation emitter. The main energy dissipation mechanism is forming many kinds of flow patterns, such as sharp turn flow, two-ways flow and mixed flow to increase more local head loss and eliminate extra inlet pressure. These flow patterns are produced by dividing water device and blocking water device in the flow channel. This structure can enhance the effect of dividing flow, sudden shrinkage, and sudden enlargement of flow channel section. In order to study the hydraulic performance and the effects of geometric parameters on hydraulic characteristic, we arranged 25 experimental schemes according to the orthogonal experimental design method with flow index as evaluation criteria. Five key geometric parameters (distance between dividing water device and flow channel side wall, distance between blocking water device tooth and dividing water device, distance between blocking water device and flow channel side wall, maximal flow channel width of blocking water device and dividing water device, bottom pillar height of blocking water device) were chosen and to flow rate and flow index under different pressures were determined. Laboratory experiments were carried out in State Key Laboratory Base of Eco-hydraulic Engineering in Arid Area, Xi'an University of Technology. Each experimental scheme was set 5 repeats by using high-precision engraving technology and average flow rate was taken to ensure the accuracy of results. Based on the flow rate of each experimental scheme, the flow index was obtained by using multivariable regression method. At the same time, the local loss coefficient of unit flow channel was calculated on the basis of hydraulic theory. In addition, the results of orthogonal experiment were analyzed with intuitive analysis and variance analysis. Then the regression model between geometric parameters and flow index was built. The results showed that the logarithm of flow rate had a good linear relationship with the logarithm of inlet pressure (R2=0.998-0.999). Based on the relationship, the flow index for the experiment ranged from 0.432 to 0.464, indicating excellent hydraulic performance. The local loss coefficient of unit flow channel was in the range from 6.698-19.130. The energy dissipation effect of two-ways mixed flow emitter was obviously improved compared with the traditional flow channel structure with local loss coefficient of 2.1-4.8. Among the 5 geometric parameters, the maximal flow channel width between blocking water device and dividing water device was the most important influential factor for the flow index, and followed by the distance between dividing water device and flow channel side wall, the bottom pillar height of the blocking water device, the distance between blocking water device tooth and dividing water device. And the effect of these factors on the flow index was significant. However, the distance between blocking water device and flow channel side wall did not significantly affect the flow index. And the regression equation based on the parameters and flow index was well established with R2 of 0.94 (P<0.01). The regression model was verified using the hydraulic experiments with the other three groups of structure parameters. The relative error of estimated and experimental flow index was from -0.46% to 1.17%, which verified the accuracy and reliability of the regression model. These conclusions can provide theoretical evidence for structure design, pre-research and evaluation of hydraulic performance of two-ways mixed flow emitter.