Mechanism Of The Emitters Chemical-clogging Under Drip Irrigation With Saline Water And Its Preventation Mehtods

The use of saline water for agricultural irrigation has become one of the most important methods for addressing the current global water shortage, and drip irrigation is considered the most effective and reliable method for using saline water resources. However, there are high levels of salt in saline water, which results in easy recombination during transport and therefore chemical clogging. It severely restricts the development of large scale drip irrigation projects. In this dissertation, the emitter chemical-clogging behaviors and their suitability for saline water drip irrigation were explored. The electrochemical、Field Scanning Electron Microscope (FESM) were combined to quantitative and qualitative analyzed the clogging materials internal emitters. A hydrokinetic model for clogging materials growth of drip irrigation emitters was proposed. Based on drip irrigation on-site experiment, field cultivation trials and Computational Fluid Dynamics (CFD), considering the running model, water quality and flow path structure of emitters, the control methods for chemical-clogging were proved. The main results include:(1) We analyzed the chemical-clogging characteristics of different drip irrigation emitters. The results showed as the running time increased, the discharge ratio variation (Dra) and coefficient of uniformity (CU) both declined. The Dra and CU of cylindrical emitters decreased gently, while those of flat emitters showed a "slow-fast" downward trend. Cylindrical emitters with higher flow showed better anti-clogging capacity.(2) We researched the clogging material compositon and key factor under the saline water drip irrigation. The average clogging materials distribution density showed a significant negative linear relationship with Dra and CU (R2=0.81 and 0.88). The chemical constituents of clogging materials for all treatments all same, included Ca+Mg carbonates (CaCO3-R, CaCO3-0, CaMgCO3 and CaMg(CO3)2), silicates (Mg5Al(Si3Al)O10(OH)8 and NaAlSi3O8), quartz(SiO2) and sodium chloride (Nacl). The main material responsible for emitter clogging was Ca+Mg carbonate deposits, which accounted for> 88.31% of the total.(3) A hydrokinetic model for clogging materials growth under saline water drip irrigation was proposed. The clogging materials growth showed asymptotic curve, which include the fast growth phase and gradual growth phase. Based on the deposition and erosion of clogging material internal emitters, taking the Kern-Seaton model as prototype, considering the emitter type, geometric parameters of flow path and water quality, the constructed model could describe the growth process of clogging material well.(4) The control models for emitter chemical-clogging were provided. From the point of running model, the rotational irrigation between fresh and saline water could relieve the chemical-clogging. For all saline water irrigation, the irrigation frequency of once daily could maintained the high flow raters of emitters.For the water quality, the saline water salinity had the linear negative correlation with the Dra and CU. The conductivity could affect the chemical clogging process and distribution characteristics. The conductivity of saline water should control within 4.0 dS/m for the Hetao District. For the emitter structure, based on the CFD method, after comprehensive consideration of the hydraulic and anti-clogging performance, the optimized flow path width and depth were 1.0mm and 1.1mm. The flow path length should be less than 224.0 mm, and a series of emitters with different flow rates could be developed by changing the flow path depth.