| As the core working part of the combine harvester,the performance of the cleaning device will directly affect the operation efficiency and quality of the whole machine.This dissertation relies on the national “13th Five-Year Plan” key research and development project sub-project “research and development of high clarity harvesting technology and equipment for vegetable seed breeding”.Taking Chinese cabbage with the largest vegetable planting area in China as the research object,aiming at the problems of low mechanization and high labor cost in the large-scale seed production of Chinese cabbage,based on the systematic analysis of the physical and mechanical characteristics of each component of the mechanized harvesting and cleaning mixture of Chinese cabbage seed,the method of “fan-sieve-roller combined”cleaning was proposed.Applying the theory and method of computational fluid dynamics,the material particle group model of cleaning mixture and its motion equation under the action of airflow field,separating sieve and accelerating roller were constructed,and the working mechanism of fan-sieve-roller combined cleaning device was proved.Based on theoretical analysis and calculation,a fan-sieve-roller combined cleaning device was developed.The bench performance test of the cleaning device was carried out,and the mathematical model of the motion parameters of the device structure and the cleaning index was established,which laid a theoretical foundation for the improvement of the cleaning performance of the mechanized harvesting of Chinese cabbage seed.This dissertation mainly has carried on the thorough research in the following aspects:1.Mastered the physical and mechanical properties of Chinese cabbage seed plants and their mechanized harvesting and cleaning mixture.Through the analysis of Chinese cabbage seed planting pattern and plant characteristics,it provides a reference for the cognition of each component of mechanized harvest cleaning mixture.The mechanical parameters of stems,pods and grains in different parts of Chinese cabbage seed plants at harvest were tested and measured,and the changes of mechanical parameters of stems,pods and grains under different types of external forces were explored.The basic physical parameters such as geometric size,moisture content,thousand-grain weight and density of each component of the cleaning mixture for mechanized harvesting of Chinese cabbage seed and plants were measured,and the stacking angle,sliding angle and suspension speed characterizing the flow,friction and aerodynamic characteristics of each component of the cleaning mixture were studied.The discrete element particle model of different components of Chinese cabbage seed cleaning mixture was constructed by discrete element method.Combined with the numerical simulation of its stacking angle parameters,the accuracy and reliability of the discrete element model of each component were verified.2.Based on the comprehensive analysis of the physical and mechanical properties of the components of the cleaning mixture for Chinese cabbage seed harvesting,the method of “fan-sieve-roller combination” with high-efficiency and low-loss was put forward,that was to separate Chinese cabbage seed from the threshed mixtures with the introduction of airflow and rotation acceleration,in combination with the vibrating sieve.The three-dimensional model of fan-sieve-roller combined cleaning device is constructed,and the working process and mechanism of the cleaning device were analyzed systematically.Through the design and selection of the key working parts of the fan-sieve-roller combined cleaning device,based on theoretical calculation and analysis,the structure and important working parameters of the working parts such as the double-channel cross-flow fan,the vibration cleaning sieve and the acceleration roller cleaning room were determined,which provided theoretical and equipment support for the high-performance separation and cleaning of the Chinese cabbage seed harvest cleaning mixture.3.Clarified the mechanism of double-channel cross-flow fan in fan-sieve-roller combined cleaning system.Using CFD simulation method,the numerical simulation and flow field analysis of the main body of the cross-flow fan and the secondary air pipeline system were carried out respectively.Based on the BBD test method,the performance simulation test of the cross-flow fan was carried out,and the structural parameters of the fan were optimized.The reliability of the simulation optimization results was further verified by the wind speed test.CFD was used to simplify the model of fan-sieve-roller combined cleaning device and simulate the cleaning room of the device.The relationship between the internal flow field change of the cleaning room and the angle of the suction port,the wind speed and the distance between the vibrating sieve surface and the suction port was obtained by numerical simulation analysis.It plays a guiding role in the selection of key structural parameters of fansieve-roller combined cleaning device.4.The migration law and motion characteristics of each component of Chinese cabbage seed cleaning mixture in the process of fan-sieve-roller combined separation and cleaning were mastered.The separation and cleaning process of Chinese cabbage seed cleaning mixture in the device was numerically simulated by CFD-DEM coupling simulation method.The change curves of quantity and average speed of material components in different areas of combined cleaning system were obtained by simulation.Combined with the flow line distribution of gas-solid coupling material,the quantity change rule of each component of Chinese cabbage seed cleaning mixture with time in different regions was ascertained,and the movement track and average velocity change trend of each component of the material with time in different regions were explored.5.The separating and cleaning mechanism of fan-sieve-roller combined Chinese cabbage seed cleaning mixture was revealed,and the fan-sieve-roller combined cleaning device was developed.The wind speed performance test of the doublechannel cross-flow fan and the whole fan-sieve-roller combined cleaning room was carried out,and the airflow distribution law of the cleaning system and the negative pressure flow field distribution state of the cross-flow fan and the system cleaning room without material were obtained.The single factor test was carried out on the main working parameters of the fan-sieve-roller combined cleaning device.The correlation between the influence of various factors on the impurity rate and cleaning loss rate of Chinese cabbage seed was ascertained,and the value range of each factor that had a significant influence on the performance of the cleaning device was clarified.The response surface analysis method was used to establish the mathematical model between each factor and the grain impurity rate and the cleaning loss rate,with the feeding amount,the speed of the cross-flow impurity suction fan and the speed of the acceleration roller as the independent variable factors.Through the analysis of each factor and their interaction,the optimal working parameters of fan-sieve-roller combined cleaning device were obtained,and the reliability of the results was verified by experiments. |
PDF Full Text Request