Study On Anti-clogging Performance And Structural Parameters Optimization Of Bidirectional Flow Channel Emitter In Drip Irrigation

The bidirectional flow channel has good hydraulic performance.In this paper,anti-clogging performance and structural parameters optimization of bidirectional flow channel were studied by combination of laboratory experiment,numerical simulation and theoretical analysis.These researches are of great significance to improve the whole performance and speed up the research and development process of bidirectional flow channel emitter in drip irrigation.The main results of this study are as follows:(1)A dynamic evaluated index for hydraulic performance of drip irrigation emitter was proposed based on the sediment deposition process,which can synthetically reflect the dynamic variation process between hydraulic performance and anti-clogging performance.The results showed that the effect of sedim ent deposition was the main reason which caused the hydraulic performance of drip emitter degrade.(2)The scanning electron microscope(SEM)analysis indicated that the degree of sediment deposition was the most serious in the anterior segments of bidirectional flow channel,followed by the middle segments and the least in the last segments.In the anterior and middle segments of the bidirectional flow channel,the structure of sediment deposition was mainly the aggregates due to flocculation and bond which made up of fine particles filled the coarse granules.But,in the posterior segments,the structure was mainly the floc due to flocculation which made up of fine particles.Along the direction of the flow channel from front to back,the proportion of sediment particles with the size greater than 0.03 mm decreased gradually,the proportion of sediment particles with the size less than 0.005 mm firstly decreased and then increased.The results also showed that sediment particles with the size less than 0.03 mm were easily deposited in the bidirectional flow channel because of the flocculation.(3)Based on SVM theory,the relationship was built between the passage rate of particles and its affecting factors,including the working pressure,structural parameters of bidirectional flow channel,sediment equivalent particle size and the wall rebound coefficients which usually should be set in the Euler-Lagrange stochastic trajectory model.On the account of the relationship above,an optimization model of sediment equivalent particle size and the wall rebound coeff-icients identifying was established,in which the maximum of the correlation between the passage rate of particles and the relative flow rate was taken as obj ective function.And then,the numerical simulation method of liquid-solid two-phase flow for bidirectional flow channel emitter in drip irrigation was proposed based on the verification by experimental results.(4)The analytic results of numerical simulation showed that the larger the flow velocity gradient,the higher the turbulent kinetic energy,the stronger the disturbance to sediment particles which benefited to improve the anti-clogging performance of bidirectional flow channel emitter in drip irrigation.And the phenomena mentioned above became more obvious in area where the forward flow and reverse flow mixing and collision occurred.Although the flow velocity gradient was higher in whirlpool zone,the overall velocity and turbulent kinetic energy were lower.This can easily generate sediment deposition,thus the probability of emitter clogging was great.The regions where rotational motion of the traj ectories of sediment particles occurred were the main parts of sediment deposition;thereby the probability of emitter clogging was also great.The shorter the moving distance of sediment particles in the horizontal direction of the bidirectional flow channel,the better the anti-clogging performance of the bidirectional flow channel emitter in drip irrigation.(5)In order to improve the overall performance of bidirectional flow channel emitter in drip irrigation,taking hydraulic performance and anti-clogging performance together into considering,the steady flow indicator evaluating the hydraulic performance and the flow passage particle rate evaluating the anti-clogging performance were chosen as the objective functions.And then,the multi-objective optimum problem of structural parameters of bidirectional flow channel was solved by the joint use of multi-objective genetic algorithm NSGA-? and SVM algorithm in which the steady flow indicator minimum and the passage rate of particles maximum were as the optimization objectives simultaneously.The practical examples demonstrated that this method can improve the overall performance of bidirectional flow channel emitter in drip irrigation under different preferences,including working pressure ranges,rated flow demands and expectation favors of the dual objective functions.Moreover,the method had certain reference value for the research and development of series products base on the design method of bidirectional flow channel.