水稻吸湿过程的内部传质及裂纹机理研究

Study on Mass Transfer and Cracking Mechanism in a Rice Grain During Moisture Absorption

假定水稻为复合椭球体 ,在圆柱坐标下 ,利用有限元法 ,通过改进的传质模型和粘弹性力学模型 ,对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 :水稻吸湿时 ,表层含水率很快达到平衡水分 ,中心含水率变化缓慢 ;水稻颗粒中心所受拉应力最大 ,表层所受压应力最大 ,沿颗粒横向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。利用吸湿实验对模拟结果进行了间接验证。

The shape of the rice grain was assumed as an ellipsoid. In a cylindrical coordinate system, finite element simulations of the transient moisture distribution and stresses distribution in the rice grain during the moisture absorption were carried out. The results indicated that, during the moisture absorption, the outer portion of the grain was equilibrated rapidly, but the moisture content in the central portion increased slowly. The moisture absorption induced compressive stresses in the outer portion and tensile stresses in the inner portion of the grain. The fissuring of rice is more likely to be initiated at the center of the grain. The similar results were obtained in the experiments.