【作者】 米双山；

【导师】 曹崇文；

【作者基本信息】 中国农业大学 ， 农产品加工工程， 2000， 博士

【摘要】 介电分选原理是种子分选中的重要组成部分之一，它具有结构简单、适应性强、分选效果好、可接种子活力进行分级的特点。目前，国内外对其研究及应用的热度越来越高。但是，由于对该原理及其机具的研究起步较晚，许多方面的研究尚不够深入，使介电分选机在生产上未能得到大面积的应用。为此，本文通过理论分析与试验相结合的工艺路线，围绕着为介电分选机的设计开发提供依据这个中心，对介电分选机理及其设备进行了多方面的研究。 通过将种子简化为一种复合介质模型，探讨了种子的电特性，分析了影响种子介电特性的各因素以及种子的介电特性与种子活力之间的关系。通过对种子在电场中的极化情况分析，推导出了种子在电场中所受到的极化力方程。在此基础上，建立了种子在双绕线圈滚筒上的分选模型。为合理地确定介电分选机的结构参数和工况参数提供了理论依据。 在利用前人将双绕线圈简化成两根无限长平行导线的做法的基础上，将相邻以至远邻电极的影响考虑在内，建立了双绕线圈所产生的电磁场模型。将此模型与前人建立的模型进行了对比分析，并利用它对影响电磁场的各个因素进行了分析，得出了电磁场随各参数变化的规律，并提出了改进分选效果、提高分选机性能的措施。结果表明：新建的模型克服了前人所建立的模型的缺点，更符合于实际情况，它对分析各因素对电磁场的影响规律以及在介电式种子分选机的参数设计时更具有指导意义。 通过对分选电极材料和型式的研究，首创了以铝作为芯材并具有双绝缘层的电极型式。该电极的内绝缘层为聚乙烯，主要起绝缘作用；外绝缘层为聚氯乙烯，主要起保护聚乙烯的作用，同时兼顾绝缘作用。通过对电极尺寸的研究，得出了内、外绝缘层的最小厚度。在此基础上，设计了三种不同尺寸的电极，并利用由它们绕制的滚筒对谷子和小麦种子进行了分选试验，得出了“无论是分选大粒种子还是分选小粒种子，都以小直径的电极缠绕的滚筒为佳”的结论。为分选电极的正确选用提供了依据。 在将分选滚筒简化成具有电阻的电容器模型的基础上，通过理论分析分别得到了绝缘层为单层介质和双层介质的电极所组成的滚筒的电容计算公式，并通过理论计算研究了影响电容的各因素。同时，对分选滚筒所产生的电磁场的能量转换及滚筒消耗的功率进行了理论分析。在此基础上，进行了试验验证，得出了分选滚筒的电容、能量、消耗的功率随分选电压和生产率等参数变化的规律，为变压器的选型设计及分选机的功率匹配提供了依据。 通过理论分析与试验相结合，确定了双绕线圈滚筒式介电分选机的总体结构及参数，并利用试验研究确定了多滚筒介电分选机应配备的滚筒数量。在此基础上，根据带绒棉种的特点，研制了介电式带绒棉种分选机。在国内首次解决了带绒棉种的分选难题，通过利用带绒棉种在不同含绒率水平下进行的分选电压的单因素试验，得出了其分选规律。通过对不同带绒棉种的分选试验以及在生产中的实际应用证明：介电式带绒棉种分选机的研制是成功的，选后种子的各项指标都达到或超过了国家标准要求。更多还原

【Abstract】 Dielectric separation is one of the important methods to separate seed. Thedielectric separator has the characteristics of simple structure, good adaptability,reliable separating effect, and classifying seeds according to the vigor differences thatother separation methods can not match. Although much attention is being paid ontheory and application both in China and abroad, the dielectric separator has not beenwidely used in seed production. This is because the principle of seed separation usingthe dielectric property is new and the researches in many aspects have not been donethoroughly. Therefore, the purpose of this study is to provide scientific basis fordielectric separator design and development through theoretical analysis andexperimental researches.Based on modeling the seed as a compound substance, the dielectric property ofthe seed was studied. Meanwhile, the factors affected the dielectric property of seedand the relationship between the dielectric property and seed vigor were bothanalyzed. By analyzing seed polarization in the electric field, the polarization forceformula of the seed was developed. The seed separation model on the bifilar-winding-cylinder was developed, which provided scientific basis for determining bothstructural and operational parameters for the dielectric separator.The previous model for electric field intensity of the bifilar-winding-cylinder wasdeveloped by means of simplifying the bifilar winding into two parallel infinitely longwires, and was widely applied. We developed a new electric field intensity model withthe similar method, but taking into account the electric field intensity produced byboth the neighboring electrodes and the other electrodes. Comparative analysisbetween the new model and the previous model was made. The new model was usedto examine the factors affecting the electric field intensity and the relationshipbetween electric field intensity and the parameters of the bifilar winding wasestablished, and measures to improve separating effect and to increase separatorperformance were presented. Since the model eliminates the weaknesses of the*previous model, it is more practical, more accurate in analyzing the effect ofparameters on the intensity of electric field and in designing the seed separator.Based on studies on electrode material and electrode construction, a newelectrode was designed, with aluminum as conductor and two layers of insulation.Polyethylene is used as inner insulation material to provide insulation and polyvinylchloride is used as the outer insulation material to protect polyethylene and provideinsulation as well. The minimum thickness for both the inner and outer insulationlayers was decided. Cylinders made from three electrodes of different sizes were usedto test the separation effect on wheat and millet seeds. "Whether small seeds or largeII2seeds, the cylinder with the smallest size electrode shows the best separation effect",which provides the scientific basis for accurate application of the electrode.On the basis of simpli1~ying the separating cylinder as a capacitor model withresistance, the capacitance formula for cylinders with single-insulation-layer electrodeand two-insulation-layer electrode were established respectively. Factors affecting thecapacitance were studied, energy of the electric field and power consumption of thecylinder were analyzed. Laboratory experiments were conducted to test and verify thetheory. The capacitance, energy, power consumption of the cylinder as a function ofseparating voltage and productivity were determined, which provided scientific basisfor the design of the transformer and power matching of seed separator.Based on the theoretical analysis and experimental studies, structural andoperationa更多还原