| Venturi fertilizer applicator due to its obvious advantages such as: simple structure,low cost and without an external power has been widely used in micro-irrigation system.However,in practice,the fertilizer concentration is fixed and is difficult to achieve automatic adjustment of fertilizer concentration because it restricts the range of device.Most of all,it is difficult to directly apply to the automatic control system of irrigation and fertilization.There for,in this thesis first CFD numerical simulation and experiment methods used to optimize the structure parameters of Venturi fertilizer applicator,then Venturi fertilizer applicator sample designed,and the ball valves in 3 positions of inlet,outlet and fertilizer suction of Venturi fertilizer applicator installed.In order to obtain the best control method for variable fertilizer concentration of Venturi fertilizer applicator the experiment testing and analyzing the regulation performance of the 3 kinds of controlling methods conducted,that showed the best control method is to control the variable concentration of Venturi fertilizer applicator,it can provide the theoretical basis for the application of the Venturi fertilizer applicator to the variable regulation of fertilizer application in the automatic control system of irrigation and fertilization.The main research work and conclusion of this thesis are as follows:(1)Based on(CFD)numerical simulation analysis method,using Fluent 16.2.0,Solidworks2015 and Gambit2.4 software,with inlet pressures range of 0~0.3 MPa,10 combinations of the structure parameters of Venturi fertilizer applicator such as: contraction angle α,diffusion angle β,inlet diameter a,outlet diameter b,A fertilizer suction tube diameter,B length of inlet section,C length of outlet section,λ throat diameter ratio,θ throat length to diameter ratio and γ suction tube angle were optimized and analyzed.From fertilizer absorption efficiency and fertilizer concentration the optimum combinations of the structure parameters of Venturi fertilizer applicator obtained: a=b=25 mm,A=6.25 mm,B=C=20 mm,λ=0.25,α=25°,β=7°,γ=135°,θ=1.5,then the sample was manufactured by 3D printing technology,and the fertilizer absorption performance was verified through experiments.(2)The Venturi fertilizer applicator sample was placed in the pipeline system,and the ball valves were installed at the inlet,outlet and fertilizer suction of Venturi fertilizer applicator respectively.A pressure gages and flow meters were used to set up the experiment platform for controlling the performance of the fertilizer concentration of Venturi fertilizer applicator,and the control of fertilizer concentration being by adjusting the ball valves angle under inlet pressure range of 0~0.2MPa,and the control performance of the 3 control methods is tested,and the opening ball valve angle in each method from 0~90° every 5°.The adjustment of inlet pressure is achieved by changing the height of the water tank.The opening of the valve angle is determined by the self-made dial installed on the ball valve.(3)The results of the 3 control methods showed: In inlet section adjusting ball valve angle 0~70° can control the fertilizer concentration continuously.The fertilizer concentrations decrease with reduction in inlet pressure 10.976%~0%.Also there were vibrations when the pressure was high and the valve angle was 0°,this had affected in fertilizer concentration;In outlet section adjusting ball valve angle 0~60° can control the fertilizer concentration continuously.The fertilizer concentrations come down with reduction in inlet pressure 10.946%~0%.Also there were vibrations when the pressure was high and the valve angle was 0° this also had affect in fertilizer concentration,beside returning water to fertilizer tank when the valve angle was 65~90°;In fertilizer suction,can control the fertilizer concentration continuously by adjusting ball valve angle 0~75°11.731% to 0.139% the fertilizer concentration increase with closing valve angle 0~20° and the highest fertilizer concentration recorded was 11.731% with 20° valve angle,then the concentration come down with closing valve angle beside the concentration also come down with reduction in inlet pressure 11.731%~0.139%.But the vibrations in this section were less than inlet and outlet sections.(4)From the fertilizer concentration,fertilizer absorption efficiency and the performance of the Venturi fertilizer applicator,the comprehensive comparison of the 3 control methods can be concluded that the optimal performance of variable rate of fertilizer concentration obtained at the fertilizer suction,and the automatic control device can be installed at the fertilizer suction of the Venturi fertilizer applicator for the automatic control of the variable fertilizer concentration. |
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