稻谷籽粒内部热湿传递三维适体数学模型研究

摘要

针对稻谷热风干燥过程中出现爆腰,而其机理又尚未明确的问题,以图像法构建稻谷籽粒三维适体网格,TPS法测定导热系数,逆推法计算水分有效扩散系数,利用COMSOL Muhiphysics软件模拟计算热风干燥过程中稻谷籽粒内部的温度和水分分布,并与实验结果对比.结果表明:三维适体数学模型具有较高的精度,干燥过程中稻谷籽粒干基含水率模拟数据与实验数据最大误差低于8％;稻谷籽粒内部温度和水分分布梯度沿径向(短轴)比沿轴向(长轴)大,且水分梯度维持时间远大于温度梯度;沿籽粒径向由外表面至中心1/3长度内的水分梯度较径向其它部分的水分梯度大,与实验观察的爆腰由籽粒表面向内扩展相吻合.研究结果为准确预测籽粒内部的干燥应力,揭示稻谷爆腰机理提供了基础.%Rice cracking occurring in the hot air drying of rice kernels reduced its quality and economic values.The reason for the rice cracking is due to the local drying stress of the kernel exceeds its resistance.The drying stress includes the stresses induced by temperature and water gradient,so the temperature and water gradient is basis for predicting drying stress.The purpose was to predict the heat and mass transfer process inside the rice kernel.The image processing technology was applied to construct a three-dimensional body-fitted grid for the rice kernel.The governing equations and relative boundary conditions were developed for the heat and mass transfer processes respectively.New measuring technology (TPS) was used to measure the properties of rice kernel such as the heat conduction and mass diffusion coefficient.Finally,the Comsol Multiphysics software was applied to solve the mathematical model.The simulation results were compared with the experimental data and the difference was less than 8％,indicating high model accuracy.The temperature and water distribution gradients in the rice kernel along the radial direction (short axis) were larger than those along the axial direction (long axis),and the duration time of water gradient existence was longer than temperature gradient existence.The moisture gradient in the radial direction from the outer surface to the one-third of center was larger than that in other parts of the radial direction,which was consistent with the cracking phenomena observed in experiments—the crack extended from the surface inward.The image processing technology was applied to construct three-dimensional body-fitted grid for the rice kernel.New measuring technology (TPS) was used to measure the properties of rice kernel.