Inline Mixers For Applying Liquid And Solid Pesticides And The Performance Evaluation

Inline mixing application of pesticides of differing physical states could achieve variable-rate spraying while decreasing excessive waste and environmental pollution,and avoiding direct human-chemical contacts.Conducting researches on inline mixers and performance evaluations of them could provide feasible technical solutions to the precise and variable-rate application.Initially,based on theoretical analysis,the inline mixing process of liquid pesticides and water was researched to design several kinds of mixer structures that promote the uniform mixing for liquid pesticides,and meanwhile alleviate the concentration inconsistency under the condition of pulsated pesticides injections.According to the results,it could be concluded that stronger turbulence intensity improved the mixing efficacy,dispersed pesticides injection would help reduce the mixing length required for uniform mixing,and that increasing pesticide injection dosage would increase the distribution probability of pesticides around the detection tube.It was necessary to rely on the turbulent mixing effect and pulsation attenuation structure to improve pesticides concentration consistency on time series under pulsated pesticides injections.To alleviate the concentration inconsistency,a layered mixer?B?with a perforated tube to attenuate the concentration pulsation was developed.Being different from the venturi jet mixer?A?in the principle of turbulent diffusion for mixing pesticides,multi-injection of pesticides on the cross sections of the mixer B achieved the uniform mixing of the pesticides directly.A layered mixer with the mixing tube?C?,which was a combination of the structures of mixer A and mixer B,and a simplified layered-jet mixer?D?were also developed in this process.The mixer D could also be regarded as an optimized venturi jet mixer with structures of mixer B.The principal component analysis?PCA?algorithm by image processing could measure mixing uniformity,of which the results is almost consistent with that obtained from CFD simulations.The increasing carrier flow rates?Q?could cause improvements of mixing efficacy,but the change caused by varying Q from 800mL/min to 2000mL/min was not as significant as that by varying mixing ratios?P?from 1:100 to 10:100.The mixing uniformity in mixer A decreased clearly with an increase of P because the pesticides concentrated gradually on one side of the detection tube.The mixer B performed better than mixer A,especially at high P.Mixer C,whose structure was a combination of those of mixers A and B,achieved the optimal mixing efficacy but with the most complicated structure.The uniformity in the mixer D(H_ave=12.46)obtained by simplifying mixer C was superior to those in mixers A(H_ave=15.35)and B(H_ave=14.65)but inferior to that in mixer C?Have=4.08?.With a relatively simpler structure,mixer D might generally meet the uniformity requirements although further structural optimization of it seemed necessary.The coefficient of variation on time series?CVT?could be applied for evaluating the concentration inconsistency.Auto-correlation?R?and approximate entropy?ApEn?could be applied for describing the concentration pulsation with periodic characteristics and the concentration series complexity,respectively.Increasing Q,P,and even injection frequency?F?could improve concentration consistency and spraying accuracy.Concentration variability was the most obvious for mixer A with the average CV as high as 4.12%.Using auto-correlation and complexity analysis,the concentration series exhibited strong periodicity and relatively lower complexity.Concentration variability for mixer B was less prominent with an average CV value1.25%and concentration periodicity sometimes being indeterminable.Mixer D showed moderate concentration variability?CV=2.26%?although pulsation was still detectable.Mixers with similar structures to mixer D could be applied for improving the spraying accuracy.There is a positive correlation between the mixing uniformity and the dynamic concentration consistency,indicating that a more efficient mixer was needed when the injection pulsation was strong.Quantitative descriptions for uniformity inside the detection tube by CVT,which had the potentials to describe the mixing uniformity,and gray level co-occurrence matrix?GLCM?,which was further proposed to evaluate mixing uniformity,failed to reflect accurately the changing-trends in uniformity eventually.Additionally,Information entropy?HIE?-based method tended to underestimate changes,while coefficient of variance based on each single frame?CVS?underestimated it when mixtures showed stratification,indicating that both methods were not suitable.Optimized area-weighted uniformity index?OAU?and PCA proved to be more advantageous than histogram second-order moment?HSM?because these methods did not only rely on pixel probability distributions of gray-scale histograms,but the positional information of the pesticides distribution,even though the HSM was more time-efficient than them.On the basis of theoretical analysis,a multi-orifices jet mixer?MJM?was designed to satisfy the preconditions of uniform mixing when the powder pesticides were injected with airflow carriage.Preliminary tests showed that Q=1800mL/min,P_r?Pesticides inlet pressure?=0.11Mpa satisfied preconditions of airflow-carrying and inline mixing powder pesticides.CFD simulations indicated the number of injection orifices n,area ratio m and nozzle diameter dn of the MJM had significant effects on mixing uniformity,while the nozzle-tube distance Lnt insignificant.Furthermore,preferred structural parameters were determined as n=2,m=1:4,d_n=2.5mm,L_nt=4mm.Actual test results revealed the optimized MJM could significantly improve the mixing efficacy with deposition uniformity index up to 0.8123,though slightly lower than that of premixed spraying?0.8429?,but significantly higher than the situation without mixer applied?0.6657?.The optimized MJM was applicable in actual inline mixing and spraying for powder pesticides,and the proposed prototype spraying system for applying powder pesticides was feasible though further optimization on it seemed necessary.A single-orifice jet mixer was designed for applying water dispersible granules?WDG?by reducing the injection nozzles of the optimized MJM to n=1.In the inline mixing tests for WDG,the 3D image-based method to determine inline mixing efficacy of WDG was feasible.With the help of methods through single-viewing images,it could evaluate the uniformity of WDG distribution after the mixing by the mixer.Test results indicated that the uniformity of particle distribution significantly increased,and the particle amount in each sub-area of the mixing tube gradually became similar with the increase of Q and more the amount of particles???injected.The increase in particle sedimentation speed and detection distance significantly reduced the fluidization of particles,resulting in bottom aggregation of particles.The particles with more similar density to water and smaller diameters could promote the inline mixing applications of them though actual tests might be needed in the future.By comprehensively analyzing the principles of inline mixing of pesticides in liquid and solid states,applicable inline mixers were proposed and comprehensive performance evaluations for them were conducted,thus specifically addressing the mixing problems of pesticides in inline mixing and spraying systems and providing feasible solutions to the practical applications.During the research,the image-based methods to evaluate inline mixing efficacy,which were typical non-intrusive testing approaches,were also enriched.