| No customized fertilizer machines are widely applied in tea fields and traditional spreaders for field crops are constrained by the narrow row spacing of tea trees when used for tea fields. The most commonly used fertilizer spreader existing in tea field was mainly artificial fertilization. Therefore, it is of great significance to develop a fertilizer application machine which can be widely applied to the tea field. Based on the analysis of the working process and the structure of the centrifugal distributor, the mechanical parameters of the fertilizer particle were measured and the movement of it was analyzed, the process of fertilization was also simulated, then the operating parameters of the distributor were optimized by experiment, and the result was validated by field experiment. In this paper, a digital analysis method was adopted in order to explore a fertilizer distributor. The main research contents and results are listed as follows:(1) Determination of mechanical parameters of fertilizer particles The urea and compound fertilizer which are the largest demand of tea plant were investigated, the parameters such as coefficient of restitution, three axis dimension, density, stiffness coefficient and friction coefficient were measured. The result showed that the urea and compound fertilizer#s coefficient of restitution were 0.39 and 0.41; the average length were 3.80 mm and 3.42 mm, the average width were 3.57 mm and 3.21 mm while the mean thickness of were 3.59 mm and 3.19mm; the mean values of equivalent diameter were 3.64 mm and 3.19 mm. the spherical degree of the two kinds of fertilizer particles were more than 93%; the particle density of them were 1.61 g.cm-3 and 1.10 g.cm-3, the bulk density of them were 0.75 g.cm-3 and 0.90 g.cm-3; the stiffness coefficient of the fertilizer particles were 132.88 N/mm and 85.51 N/mm; the static friction coefficient were 0.59 and 0.55 while the dynamic friction coefficient were 0.54 and 0.41; the moisture content were 0.37% and 1.10%\(2) The structure design of distributor and movement analysis of the fertilizer particles The structure of the distributor was designed according to the requirement of the fertilization and the characteristics of the tea field. The structure designed in this paper is mainly composed of the fertilizer box, rack, centrifugal plate, feed opening, DC motor, auxiliary laying-off device, etc. To obtain the kinetic model of fertilizer particles during fertilization, the principle of fertilization in tea field was explained and the particle#s movement in the process of fertilization was also analyzed. The dropping outlet is designed as a horseshoe-shaped, and positioned above the outside flange outer contour. In the process of fertilization, when the fertilizer particles through to the dropping outlet, the fertilizer particles will reduce the dropping velocity due to the buffering effect of the dropping outlet. So it makes the machine more stable, and the fertilizer particle does not accumulate in the centrifugal disc center. The design of centrifugal plate#s blade was to freely adjust fertilization width and improve the spreading uniformity. The structure and size of the rock was designed according to the tractor#s front size. To make the rear rotary cultivator bury the fertilizers during the process of fertilization, the distributor should be fixed on the front of tractor.(3) The simulation of centrifugal fertilization processAccording to the mechanical parameters of the fertilizer particles, the spherical model of fertilizer particles and the geometric model of distributor were established. In order to meet the 0.8 m width, and the corresponding centrifugal disc speed is about 300 rpm. In addition, the contact model of particles and the optimal time step of simulation were also determined. The fertilizer spreading process was simulated with EDEMLand the effect of distributor forwarding speed, blade number, and blade offset angle on variation coefficient of fertilizer particles distribution was analyzed. Besides, the variation of the velocity, actual force condition and displacement of the fertilizer particle were also analyzed.The simulation results show that the operating parameters for smaller coefficient of variation were as follows: forwarding speed of 0.6 m/s, blade number of 4 and offset angle of 30 ", and the group analysis of fertilizer particles suggested that the longitudinal uniformity of the distributor is relatively uniform than transverse direction. Moreover, the analysis of the velocity, actual force condition and displacement revealed that when the fertilizer particles through the outlet, fertilizer particles will reduce the fall velocity due to the buffering effect of the outlet which can ease the impact of the high speed fertilizer particles flow on the centrifugal disk.(4) Fertilization effect test and optimization of operating parameters Bench test was conducted to explore the influence of the blade number, offset angle and walking speed on uniformity, and the interaction effects was also analyzed. The regression model of the blade number, offset angle and walking speed for the coefficient of variation was established, the objective function was optimized under the constraint condition of each factor range, and the optimal results of the bench experiment was validated by field trial. The optimal result of the various parameters for the minimum coefficient of variation are as follows: blade number of 5, offset angle of 15.72" and forwarding speed of 0.61 m/s, and correspondingly the minimum coefficient of variation is 10.30%. The field validation test shows that the distributor had a better performance under the optimal parameters, the average relative error between the measured value and the predicted value is 10.15%, the maximum relative error is 22.14%, and the uniformity of the optimal operating parameters has been significantly improved compared with the un-optimized condition. This paper offer a device special used in tea field, the digital design and parameter optimization provide a theoretical reference for the scientific and efficient fertilization, and ideal result has been obtained in the field experiment, which can be applied to the fertilization in tea field. |
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