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The Study on Cortex Resistance in Drying Process of Corn Seeds

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Tutor: ZhangShiWei;ZhangZhiJun
School: Northeastern University
Course: Fluid Machinery and Engineering
Keywords: drying,cortex,organization,mass transfer mechanism,COMSOL
CLC: S513
Type: Master's thesis
Year:  2012
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Abstract:
In the different ways drying process of many kinds of plant material, there is a common problem of the cortical resistance dominant, which is the cortical tissue of material is usually the key factor in restricting heat and mass transfer process. The common features is that the mass transfer resistance of the epidermis is high, which limits large amounts of water in the internal organization of material come through. However, due to the lack of the physical parameters of cortex itself to mass transfer, previous studies tend to deal with the cortical and endoplasmic overall of material as a continuous homogeneous medium. There is a lack of the necessary research to them in the performance differences and the resulting of mass transfer process.The topic is intended to use corn (the grain) particles as typical biological materials and takes the combination of theoretical study and experimental study as technology roadmap. Based on the topical biological materials having cortical resistance dominant mass transfer characteristics, I make a deeper understand about mass-transfer mechanism happened inside the cortical tissue. And through making quantitative representations to the transfer performance of the cortex itself, it reveals that the cortical tissue is one of the most important mass transfer resistances in the drying process.Consider corn as a uniform porous medium structure in this paper, it use heat and mass transfer theory of porous media, set up heat and mass transfer coupling model considered cortical resistance influence and it use COMSOL simulation. From the simulation results, it can be seen that the water of cortical surface dry quickly when considering cortical impact, but the water in the endoplasmic dry slowly due to the obstruction of the cortical tissue proliferation. The smaller the diffusion rates of the cortex, that is to say, the stronger the resistance of the cortex, the more difficult water diffusion and penetration in the endoplasmic. Meanwhile, I take hot air drying experiment of the corn. I obtain cortical resistance dominant mass transfer characteristics with dealing with experimental data.I select two varieties of Shen He209and Liao Yu62maize with different moisture contents to take peeled and skin experiments, fit the results of the experimental data and simulation of corn to determine the diffusion coefficient of the different varieties and moisture content of maize seeds. It proved that the different varieties of corn seeds have differences in the diffusion coefficient. At the same time, the corn moisture content also affects the diffusion coefficient, the diffusion coefficient of the corn seed reduced with increasing water content of corn when the corn moisture content is high.The research of this subject is the principal contradiction and nature factors of the mass transfer problem for corn seed in the drying process. It explains the mass transfer mechanism in a deeper level and enriches the mass transfer theory of typical biological materials in drying technology and provides theoretical support for energy-saving study of drying technology.
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