【作者】 刘斌；

【导师】 毛志怀；

【作者基本信息】 中国农业大学 ， 农产品加工及贮藏工程， 2000， 硕士

【摘要】 本文对谷物干燥和吸湿过程中内部传热传质机理进行了较深入的研究和探讨。将水稻颗粒假定为复合椭球体，在圆柱坐标下，利用有限单元方法，通过改进的传质模型和粘弹性力学模型，对干燥和吸湿环境下水稻颗粒内部水分分布和应力应变分布进行数学模拟。模拟结果表明：干燥过程中，由于表层很快失水，内部水分向外扩散缓慢，使得水稻颗粒内部处于“外拉内压”的应力状态；吸湿时，表层含水量很快达到平衡水分，中心含水量变化缓慢，使得水稻颗粒中心受最大拉应力，表层受最大压应力，沿颗粒r轴从内向外应力由受拉逐渐变为受压；水稻颗粒中心首先形成应力裂纹的可能性最大。因而可以推断干燥过程不是水稻应力裂纹形成的主要阶段，其应力裂纹的形成主要出现在干燥结束后和吸湿过程中。 试验研究了水稻在收获前、干燥过程中、干燥后存放和吸湿过程中的应力裂纹规律。结果表明，水稻田间含水量为31%时，若遇阴雨或夜间吸湿就会出现应力裂纹。干燥应力裂纹主要出现在干燥结束后的存放期间，快速干燥后谷粒内部形成的水分梯度是水稻产生应力裂纹的主要原因。水稻吸湿应力裂纹是环境温度和相对湿度联合作用的结果，稻壳具有延缓水稻吸湿的作用，从而减少应力裂纹的产生。更多还原

【Abstract】 In this thesis, the mechanism of heat and mass transfer within a grain kernel in drying or during moisture adsorption has been discussed thoroughly. The shape of the rough rice was assumed as a prolate spheroid. In a cylindrical coordinate system, finite element simulation of the transient moisture distribution and stresses distribution in the rice kernel during drying and the moisture adsorption were presented. The results indicated that, in the drying process, the surface layer of the rough rice loses moisture quickly, and the inner moisture diffusion is slowly. The drying process induced compressive stresses in the inner portion and tensile stresses in the outer portion of the rice. During the moisture adsorption, the outer portion of the rough rice was equilibrated rapidly, but the moisture content in the central portion was increased slowly. The moisture adsorption induced compressive stresses in the outer portion and tensile stresses in the inner portion of the kernel. The fissuring of rice is more likely to be initiated at the center of the kernel. It is concluded that the rough rice may be fissured after drying or during moisture adsorption.Through the experiments, the rough rice fissuring mechanism has been studied. The rough rice may be fissured pre-harvest, in the drying process,after drying and in the moisture adsorbing environment. Results indicate that the mature rough rice will induce fissuring by the moisture adsorption in the field, when the moisture content of rough rice reaches 31%. The rough rice mainly fissured after drying. The moisture gradient caused uneven shrinkage is the main reason of rice fissuring after rapid drying. During the moisture adsorption, the rice fissuring is primarily influenced by the temperature and relative humidity of air. Rough rice is more resistant to fissuring than brown rice.更多还原