| Rice is one of the main grain crops in China.In the process of rice production,side-deep fertilization technology has the advantages of labor saving,fertilizer saving,pre-promotion and yield increasing compared with conventional fertilization methods.It is an ideal fertilization technology which is suitable for rice growing areas in northern cold regions and has the function of cost saving and efficiency increasing.As the core carrier of the application of side-deep fertilization technology in rice,side-deep fertilization device has many problems,such as unstable fertilization,blockage of fertilizer pipeline and uneven distribution of nutr ients,which directly affect rice yield.In this paper,according to the agronomic requirement of rice side deep fertilization,the key components of air-fed rice side deep fertilization device,fertilizer discharger and pneumatic conveying system,were studied by theoretical analysis,numerical simulation and experimental design.(1)In order to provide an important reference for the structure design and numerical simulation parameters setting of subsequent fertilizer devices.Taking the special fertilizer for deep side fertilization of rice in northern cold region as the research object,the material characteristics of fertilizer granules were determined by combining physical experiment and simulation experiment.It mainly includes physical parameters such as density,moisture content,triaxial size,suspension velocity,elastic modulus,shear modulus and contact parameters such as elastic recovery coefficient,static friction coefficient and rolling friction coefficient of fertilizer particles.(2)According to the theoretical analysis of the filling and discharging stages,the smaller the rotational speed of the discharging wheel,the better the filling of fertilizer particles in the groove.The greater the rotational speed of the discharging wheel,the bett er the uniformity of fertilization.The maximum theoretical value of the rotational speed of the discharging wheel is 150 r/min when the filling and wrapping angle is 45 degrees.In addition,through the discrete element simulation analysis of the working process of the fertilizer dispenser,it can be seen that with the increase of the rotational speed of the fertilizer dispenser wheel,the total amount of fertilizer discharged per rotation of the fertilizer dispenser wheel decreases.When the rotational sp eed of the fertilizer dispenser wheel is higher than 60 r /min,the amount of fertilizer discharged per rotation decreases significantly.With the increase of the rotational speed of the fertilizer wheel,the change trend of the axial position of fertilizer particles is basically the same,and the The results of numerical simulation are basically consistent with those of theoretical analysis.(3)According to the working conditions of deep side fertilization of rice and the material characteristics of fertilizer particles,the main design parameters of pneumatic conveying system were analyzed and determined,and the structured design of pneumatic conveying system was completed.Based on the discrete element method(DEM)and computational fluid dynamics(CFD),the mathematical equations of gas phase and solid phase are established,and the gas-solid mixing process is simulated by DEM-CFD coupling method.According to the distribution of airflow velocity field and the movement state of fertilizer particles,the a irflow velocity distribution pattern is basically the same under different velocity inlet boundary conditions,and the maximum airflow velocity appears in the air-material mixing chamber.With the increase of inlet air velocity,the movement speed of fertilizer particles increases gradually,the bouncing phenomenon decreases,and the distance between two adjacent fertilizer particles increases gradually along the direction of air flow.(4)In order to further analyze the effect of operating parameters of fertilizer device on fertilization performance,bench test was conducted to study the fertilization stability and uniformity of fertilizer device by means of experimental design and analysis.Through single factor experiment,the change rule of fertilizer output of fertilizer device in the same time under different rotational speed of fertilizer discharging wheel was obtained.When the current feed rate was 1 m/s and the fertilizer application rate was 150 kg/hm2,the rotational speed of fertilizer discharging wheel was 16.15 r/min,and the coefficient of variation of fertilization stability was 4.71%.Through the quadratic orthogonal rotation combination experiment,the influence rules of the rotational speed of the discharging wheel,the forward speed and the wind speed of the fan on the mean value of fertilization uniformity and the coefficient of variation of fertilization uniformity were obtained respectively.The contribution rate of each factor to the mean value of fertilizer application uniformity is in the order of forward speed,rotational speed of fertilizer discharging wheel and wind speed of fan.The contribution rate of each factor to the variation coefficient of fertilizer uniformity is in the order of rotational speed of fertilizer discharging whe el,forward speed and wind speed of fan from large to small.Then,through the establishment of multi-objective optimization model,the optimal combination of parameters was obtained when the average target value of fertilization uniformity was 0.45 g: the rotational speed of fertilizer discharging wheel was 21.96 r/min,the forward speed was 0.93 m/s,the wind speed of fan was 22.93 m/s,and the variation coefficient of fertilization uniformity was 28.25%.The results of bench tests show that the relative e rror between the experimental value and the theoretical optimum value is less than 4.44%,which shows that the optimum parameters of the software are accurate and feasible.(5)In order to test the practical performance of the fertilizer device,field performance tests were carried out on the vehicle-mounted platform of Kubota 2ZGQ-6D(NSPU-68CMD)high-speed rice transplanter.The deviation of fertilizer application amount and the size of fertilizer application position were measured.When the speed of transplanter is 1 m/s,the rotating speed of fertilizer wheel is 50 r/min and the wind speed of fan is 32 m/s,the deviation of fertilizer application is controlled within 4.74%,which indicates that the overall stability of fertilizer application is high.The average minimum distance of lateral measurement was 32.87 mm,and the qualified rate was 93.33%.The average value of maximum distance of lateral measurement was 47.73 mm,and the qualified rate was 93.33%.The minimum value of the positive measurement dist ance is 55.13 mm,and the eligibility rate is 86.67%.The maximum value of the positive measurement distance is 75.13 mm,and the eligibility rate is 96.67%.The average values of the measured distances at the fertilization sites were within the eligible distances,and the overall eligible rate was 73.33%.This indicated that the fertilization location of the fertilizer device basically met the agronomic requirements of deep side fertilization of rice.This paper provides technical reference and theoretical support for further research on rice side deep fertilization device,which will effectively promote the popularization and application of rice side deep fertilization technology and accelerate the whole mechanization process of rice production. |
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