【作者】 杜建强；

【导师】 杨世昆； 刘贵林；

【作者基本信息】 中国农业机械化科学研究院 ， 机械设计及理论， 2014， 博士

【摘要】 我国传统牧草收贮工艺导致牧草在田间干燥期间干物质损失严重和营养成分保有率大幅度降低,收获后的牧草有效营养成分保有率仅为50%,在收获过程中牧草(苜蓿)的干物质损失高达30%其损失十分巨大。由于在牧草收获季节,采用牧草田间干燥法,虽然省钱,但干物质和营养成分损失严重。如果采用高温快速烘干设备,产品质量提高,但成本费用增加,且污染环境。因此,在牧草收获中,牧草干燥已成为生产优质干草最为关键的制备工艺。本文从太阳能牧草干燥湿法收获工艺入手,考虑能耗和营养成分得失,提出了采用透射聚光型太阳能空气集热器干燥牧草的新方法,并从该太阳能集热器在牧草干燥领域中的应用基础理论,光热转换效率、经济性,牧草干燥系统设备设计、干燥工艺等方面展开以下研究工作：(1)根据菲涅尔透镜光学原理,建立了透射聚光型菲涅尔透镜的三维模型,通过该模型对透镜的入射角度、焦距误差、追踪误差和加工误差进行了分析计算,得出了这些因素对透镜聚光比和在平板吸收器上聚焦光带能量分布的影响；对菲涅尔透镜加工制作过程进行了原理阐述,并进行了聚光性能和接收角的实验研究。理论分析和实验测试表明：吸收器接受聚焦光线开口尺寸为5cm,开口接收角一般控制在-0.4°～+0.4°之间时可以获得较高的光学效率。(2)应用理论分析和实验,对半圆形、圆弧形、三角形和方形四种不同几何形状的聚焦吸收器开展了研究,四种吸收器的光学性能和热力学性能显示,三角形吸收器显示出更好的光学效率和较小的热损失。因此,选择了三角形和方形吸收器进行了结构优化分析,结果表明在采用平板菲涅尔透镜作为聚光器时,三角形聚焦吸收器接受聚焦光线开口深度在4cm时最好,方形聚焦吸收器的接收聚焦光线开口深度在2cm时最好。根据优化分析结果,试制了长度为6.4m的两种吸收器。(3)研制了采光面积25.6m2透射聚焦型太阳能空气集热器,包括集热器箱体、机架支撑和控制传动装置,通过单片机控制系统实现了集热器对太阳的单轴有效追踪。当集热器箱体设计为平板菲涅尔透镜和三角形聚焦吸收器组合时,太阳能集热器的性能最佳,在一个小时内,集热器就可以从环境温度升至最高温度201℃最高温度,其空晒性能参数0.3℃m2/W。在集热器箱体内,流场分布均匀,进风加热箱体内部温度场和气流分布均匀,未出现某一区域数值超高的现象,表明集热器结构合理。(4)对固定式和单轴追踪式的集热器进行了阵列排布方式的理论分析,计算了各种阵列排布的最优集热器间隔距离,并建立了理论设计计算公式,对实际工程应用中集热器的阵列排布和设计计算提供设计计算方法。(5)试制了透射聚光型太阳能草捆干燥特性试验台,并进行了苜蓿草捆干燥特性试验,试验结果显示草捆内部苜蓿的表面温度分布和含水率的变化与干燥气流的分布有很大的关系,草捆内部干燥具有不均匀性；通过对太阳能草捆干燥设备的性能试验,得出牧草湿法收获工艺可减少干物质损失近30%,牧草的有效营养成分如粗蛋白、粗脂肪等保有率由50%提高到了90%以上。更多还原

【Abstract】 According to traditional forage storage process in our country, during drying forage dry matter loss. Forage nutrient retention rate is low in the field. Post harvest forage effective nutrient retention rate is only50%. In the process of harvesting forage (alfalfa) dry matter loss reached30%.The annual forage loss is large. In the forage harvesting season,the natural drying although saving money, but the quality of the products is low and the waste is rich in nutrition. By means of high temperature fast drying equipment on forage drying, the quality of the products is high, but the cost is high and the environment is polluted. Therefore in the forage harvesting, the drying process to produce high quality hay grass has become the most important preparation process. Starting from the solar energy forage drying wet harvest technology, the consumption of energy and nutrients losses are mainly considered.This paper presents a new method using the transmission type solar air collector dry forage. In the solar energy collector applied to forage drying field, from the application of basic theory, the photothermal conversion efficiency, economy and forage drying equipment design, drying process, the following research works are carried out:(1) According to the Finel lens optical principle,3D models transmission focus Finel lens is established. Through the lens model, incident angle, focal length error, tracking error and machining error are calculated. Effects of these factors on the ratio of lens and energy distribution of focusing light on the plate absorber is drawn. Finel lens fabrication process is described. And the experiments are carried out to study the optical performance and receiving angle. Theoretical analysis and experimental results show that:When the absorber openings size is5cm and openings receiving angle is within±0.4°, absorber can obtain higher optical efficiency.(2) Absorber is designed.Half round, arc, triangle and square four different geometries of the absorber is studied from two aspects of theory and experiment. Optical properties and thermodynamic properties of four kinds of absorber is displayed. Triangle absorber shows better optical efficiency and small heat loss. Therefore the square and triangle absorber was selected for the structure optimization analysis. The optimization results show that the triangular absorber accept focus light opening depth in4cm is best when the flat Finel lens as a condenser. Receive focus light opening depth of square absorber is the best in the2cm. According to the optimization results, two kinds of length6.4m absorber are made.(3) Daylighting area25.6m2transmission concentrated solar energy air collector is developed. Solar air collector comprises a heat collector box, frame support and control gear. Through the single-chip microcomputer control system, the collector can be single axis sun tracking accuracy. When the collector box is designed combined plate Finel lens and triangle focusing absorber, the performance of solar collector is the best. In one hour, the collector internal air drying temperature from ambient temperature rise to the highest temperature201℃. Collector air drying performance parameters are0.3℃m2/W. In the heat collector box, flow field distribution is uniform. In the heating box temperature and air flow distribution is uniform. A high numerical regional does not appear. The collector has reasonable structure.(4) The collector of fixed and single axis tracking is analyzed array arrangement. Optimal array collector distance is calculated. The theoretical design calculation formula is established. Provide a method to calculate the array to the collector in the practical engineering application and design(5) Through the construction of transmission type solar drying bale characteristics test equipment, the drying characteristics of bale was done. The test results show it have a great relationship between distribution of surface temperature distribution inside alfalfa bale and drying air flow. But also distribution changes in moisture content and drying air flow has a very close relationship. Drying is non-uniform in the bale internal. The performance test on the drying equipment show grass wet harvest technology can reduce the loss of dry matter nearly30%. Effective nutrient content of forage such as crude protein, crude fat is saved and preserved rate increased from50%to90%.更多还原