Evaluation Of Hydraulic And Anti-clogging Performances And Structural Optimization Of Labyrinth-Channel Emitters

Labyrinth-channel emitters are widely applied in drip irrigation systems for such advantages as simple structure, high hydraulic performance and low manufacture cost among those pressure non-compensating emitters. However, due to their small size of the labyrinth channels, labyrinth-channel emitters are apt to clogging. Hydraulic performance and anti-clogging performance, therefore, are two important factors evaluating the quality of emitters. In this dissertation, the hydraulic characteristic and clogging mechanism of labyrinth channel are analyzed respectively, and new evaluation methods for both hydraulic and anti-clogging performances are developed. Finally, a multi-objective structural optimization model for labyrinth channels is proposed according to the relationship between hydraulic and anti-clogging performance.The hydraulic characteristic of labyrinth-channel emitter is numerically analyzed by both laminar flow and turbulence models respectively, and a comparison is made between the computational results by the two models. The analysis of the flow field distribution in labyrinth channels showed that the transitional Reynolds number from laminar flow to turbulence is much lower than 2300, a mathematic relationship is consequently established between critical Reynolds number and the key parameters of triangular labyrinth channel based on this result. On the other hand, the experiments on hydraulic performance of triangular and trapezoidal channel emitters are carried out to verify the predicted accuracy of numerical analysis from the macroscopical view and the applicability of laminar flow and turbulence model. In addition, the flow visualization system is constructed and the flow field behavior is visualized in labyrinth channels, which verify the accuracy of numerical simulation from microscopical perspective.In an overall consideration of the major and minor losses of labyrinth channel unit, a single variable, pressure loss coefficient (PLC), is presented to evaluate the hydraulic performance of emitters. Parameterized design method and orthogonal experiments method are introduced to study the relationship between the key parameters of labyrinth channel and PLC, the influence degree of each factor ranks as follows:α> S/H > H/D > D/W, and a model is regressed between them using the linear multivariable regression method. In addition, the key parameter of main-flow channels, the ratio of arc radius to the length of straight line, is discussed with PLC in order to validate the evaluation methods. The result shows that the PLC increases as the ratio decreases, which is coincident with the idea of main-flow channel.The liquid-solid two-phase flow in labyrinth channels of emitter is numerically simulated by using the stochastic trajectory model and Eulerian-Eulerian model. The trajectories and potential deposition regions of solid particles are obtained, which can be used to explain the clogging mechanism of labyrinth channels. And then the experiments on particle deposition and particle motion are performed to compare with the analysis of two-phase flow. According to the stochastic trajectory model, an evaluation method for anti-clogging performance of labyrinth channels is proposed by introducing the variable of passage rate of particles (PRP). The analytic results show that the key parameterαis the most important factor on PRP, and then D/W, H/D is least, and another mathematic model between the four key parameters and PRP is regressed. Furthermore, the evaluation method is also tested for main-flow labyrinth channels. The PRP increases as the ratio of arc radius to the length of straight line increases, which is in accord with the design idea of main-flow channels.Considering the contradiction between hydraulic and anti-clogging performance of the labyrinth-channels emitters, PLC evaluating the hydraulic performance and PRP evaluating the anti-clogging performance are chosen as the optimization objectives, and multi-objective genetic algorithm NSGA-II is employed to solve the Pareto fronts of key parameters of trapezoidal and main-flow channels. The trade-off solutions can be obtained by calculating the minimum value of the function according to the weights of equations. This optimization method is well applicable for the labyrinth channels with the same shape but different dimensions, which benefits to the structural finalization of emitters with high performance.