Effect of optimization forms of flow path on emitter hydraulic and anti-clogging performance in drip irrigation system
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This study aims to solve the problem of emitter clogging by optimizing the flow path boundary and making it self-cleaning, thereby reducing cost of drip irrigation project to promote water-saving irrigation technologies. To resolve the question of whether the emitter optimizations should retain the vortex area with low velocity, which are the two main optimization ideas currently, we used computational fluid dynamics (CFD) analysis to evaluate the most commonly used emitter, one with a tooth-type labyrinth flow path. A re-normalization group (RNG) k–ε turbulence model was used to evaluate two types of main channel anti-clogging designs, whose vortex was retained, and three types of washing walls—all types that use a vortex. The result of the flow state analysis showed that, as for the hydraulic performance, the flow state indexes of flow paths optimized by two types of design method were up to 5% lower than that of prototype’s flow path. Flow coefficients of the flow path optimized using the main channel design method were 4–6 times higher than that of the prototype’s flow path, which could significantly increase the construction cost of emitter and drip irrigation system. However, the flow coefficients of flow path optimized by design method of washing wall with vortex were up to 3% lower than the prototype’s flow path; thus, their effect on the emitter’s hydraulic performance can be ignored. As for the anti-clogging performance, there was nearly no vortex area formed in the flow path optimized by the main channel design method, and the sediment could flow out easily from the emitter. However, the emitter’s ability to resist biological and chemical clogging was weak, because the sediment content was highest in the tooth-tip facing-water zone where the sediments deposit easily. The overall intensity of turbulence was lower than that of the prototype, and the velocity near the wall was lower than in other optimized forms. The design method of washing wall with vortex could make the vortex fully develop in the flow path, and enhance the velocity near wall and turbulent intensity in the area where sediment deposited easily. The cycle motion of vortex could wash the wall, which could keep the viscous clogging material from attaching the wall and promote their detachment. The emitter’s self-cleaning ability was also enhanced. Overall, the flow path optimized by design method of washing wall with vortex could enhance synergistically hydraulic and anti-clogging performance in the easiest and most cost-effective way. As for the tooth labyrinth flow path, the best boundary optimization form was that the tooth-tip backing-water zone, tooth-tip facing-water zone, tooth-root backing-water zone and tooth-root facing-water zone were optimized by the same arc whose radius was equal to 1/2 width of the flow path. This study could provide theoretical reference for emitter structural design.
We are grateful for financial support from the National Natural Science Fund of China (51479197, 51321001), the Special Scientific Research Fund of Public Welfare Profession of China (201401078), and the major science and technology projects in Inner Mongolia (117-05). The first author also appreciates the financial support from the China Scholarship Council (CSC) as a visiting PhD student at the University of Illinois at Urbana-Champaign.
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