Optimization And Simulation Of Structural Parameters For Venturi Injector With Large Suction Amount

Venturi injector is one of the most frequently-used fertilizer applicators for the integrated technology of water and fertilizer.It has been widely used in small irrigation systems and fertilizer applicators in China.However,in practical applications,Venturi fertilizer applicator generally still exist some problems such as low fertilizer absorption efficiency,or small fertilizer absorption.In addition,when the working pressure difference is too large,it often result in big vibration and noise,which reduces fertilizer application efficiency.How to optimize the internal structure design of Venturi injector to reduce the head loss under the same amount of fertilizer absorption,or to increase the fertilizer absorption amont under the same head loss,has become the focus in the field of fertilizer equipment research and development.The experimental testing and modeling simulation research were carried out to assess the comprehensive performance of Venturi fertilizer applicator in terms of fertilizer absorption performance,hydraulic performance,pressure loss and cavitation characteristics.Firstly,the comprehensive performance indicators including pressure energy consumption,fertilizer absorption efficiency,vibration and cavitation,were tested and analyzed,and the internal movement law of typical complex structural of Venturi injector was explored using CFD simulation model;Secondly,the asymmetrical and symmetrical Venturi injector proposed by some scholars was simulated and explored.The internal reasons for the differences between the asymmetrical and symmetrical Venturi fertilizer applicator in terms of fertilizer uptake,internal fluid movement and cavitation were studied and analyzed;Based on workbench simulation platform and OAISIS Intelligent optimization software,the optimization range of key structural parameters of PL Venturi fertilizer applicator was attained with the goal of maximizing the suction amount.The fertilizer absorption model was validated by 3D printing technology,and the five-channel layout of two common pipe layouts of fertilizer applicator,bypass fertilizer and bypass fertilizer absorber,was also studied.The effect of different pipe arrangement on the fertilizer absorption performance and channel number of Venturi injector was studied and analyzed.The main conclusions were as follows:(1)Critical pressure difference has obviously positive correlation with inlet pressure,and the maximum suction amount for homemade Venturi injector is less than that of abroad universally for the same inlet pressure.The cavitation and vibration phenomenwon of homemade Venturi injector is sensitive to variation of pressure.For the same mold size,the material with low mold shrinkage performance has smaller manufacturing error,and its suction performance is better.UPVC could be recommended as one of the proper raw materials for the manufacture of Venturi injector.In addition,each Venturi inj ector has the theoretic upper limit of the suction amount corresponding with its internal structure parameters.The cavitation was strengthened with working pressure differences increased,which was one of the important reasons for the no further improving for the maximum fertilizer absorption amont.It is an important direction of product development to minimize or weaken the occurrence of vibration and cavitation by optimizing the internal structure parameters of Venturi injector.(2)For the same amount of suction,the asymmetric structure of Venturi injector had significant reduction in energy loss compared with the symmetrical structure,and it could reduce pressure loss by 25%to 35%.The negative pressure area of the symmetrical structure Venturi injector is distributed around the throat,and the negative pressure area of the asymmetric structure venturi is distributed around the half ring,which is located in the lower part of the throat and the cavitation area is smaller in the corresponding position,which would be beneficial to increase the amount of suction under the same pressure difference.The contraction part and diffusion part of asymmetric Venturi inject are connected by the upper throat of a straight line,so multi directional velocity produces fewer collisions,and energy loss is relatively small,and the raceway of the diffusion part is also small.PL Venturi injector has a large fertilizer storage chamber,which can supply fertilizer liquid in time.Compared with other types of structure,this structure Venturi fertilizer applicator is not easy to produce cavitation.However,the diffusion section of PL Venturi fertilizer applicator is too short and its gradual change is too fast,which lead to excessive pressure loss.So there is room for further optimization and upgrading.(3)The optimal innet structural parameters was attained for PL type structure of Venturi injector,which mainly used for different nozzle diameters(3.0?5.5 mm)under an inlet pressure of 0.3 MPa and outlet pressure of 0.1 MPa.As for different nozzle diameters,the optimal range of contraction angle was 20?30°,and the optimal range of diffusion angle was 8?1°,and the optimal range of tube length was 40?50 mm,and the optimal ratio of throat diameter to weasand diameter was 1.5?1.66.In addition,the maximum fertilizer absorption amount and nozzle diameter were obtained.The regression model could be used to predict the maximum fertilizer absorption amount with different nozzle diameters.As for the same nozzle diameter(d1=4 mm),the maximum fertilizer absorption amount could be increased by about two times compared with the original model.In addition,the estimation model of the structural parameters and the fertilizer absorption amount for Venturi fertilizer applicator was established,which was verified by the three-dimensional(3D)printing samples.The model could quickly and effectively designed or predicted the fertilizer absorption amount with different structural parameters.(4)The Venturi injector with large amount suction was used in the fertilizer applicator,which was originally brought out in this paper,and compared with bypass-pushing-fertilizer pipeline,the numbers of venturi injector channels with high efficiency can be dominated by bypass-pulling-fertilizer pipeline,up to a maximum of six.Furthemore,bypass-pulling-fertilizer pipeline layout type can meet accurate ratio fertilization of more various nutrient medium simultaneously,and it can be applied to drip irrigation system that has more wide range of main pipe pressure compared with bypass-pushing-fertilizer type.When the number of channels is less than 3,the average suction amount of single channel for bypass-pushing-fertilizer type decreases with the increase of pressure,however,the average suction amount of single channel for bypass-pulling-fertilizer type could keep stable.Under the same number of channels,the total suction volume flow and proportion of fertilizer inj ection for bypass-pulling-fertilizer type is obviously higher than bypass-pushing-fertilizer type,and "three channels+bypass-pulling-fertilizer type",can be recommended as optimal pipeline layout type for fertilizer applicator with multichannel.