基于三维湿热传递的玉米籽粒干燥应力裂纹预测  

Prediction of stress cracks in corn kernels drying based on three-dimensional heat and mass transfer

作　　者：魏硕 陈鹏枭 谢为俊 王凤贺[1] 杨德勇[1] Wei Shuo;Chen Pengxiao;Xie Weijun;Wang Fenghe;Yang Deyong(College of Engineering,China Agricultural University,Beijing 100083,China)

机构地区：[1]中国农业大学工学院

出　　处：《农业工程学报》2019年第23期296-304,I0001,共10页Transactions of the Chinese Society of Agricultural Engineering

基　　金：粮食公益性行业科研专项(201413006)

摘　　要：为了揭示热风干燥过程玉米籽粒的应力裂纹形成机理,该文利用图像处理技术构建玉米籽粒的三维几何模型,将湿热传递数学模型与应力模型耦合获得应力信息,并与其屈服应力比较以预测玉米籽粒开裂特性。结果表明:该模型模拟的含水率和温度与试验值的最大误差分别为7.28%和9.64%,可以用于模拟玉米籽粒温度梯度、水分梯度和应力分布变化。干燥过程玉米籽粒的温度、水分梯度和应力表层较大而内部较小,干燥过程玉米籽粒主要受湿应力作用。干燥过程(热风温度40~80℃、相对湿度12%~52%)玉米籽粒的最大应力逐渐减小,其随着热风温度的升高而增大、随着相对湿度的升高而减小。玉米籽粒的最大应力在干燥前期大于其屈服应力而发生开裂,较低的温度和较高的相对湿度可以抑制玉米籽粒在干燥前期形成裂纹。研究结果为预测干燥过程玉米籽粒应力裂纹提供参考。Hot air drying is one of the most widely used techniques in large-scale processing of grain.However,the existing problem of grain hot air drying is the high cracking rate,which directly reduces the product grade and storage-transportation performance.It is generally believed that the formation of grain cracks is closely related to the wet stress and thermal stress during hot air drying,since the temperature gradient and moisture gradient often lead to uneven shrinkage,which induces the formation of drying stress.According to von Mises yield criterion,when the von Mises stress is larger than its yield limit,the material will fracture or develop cracks.In this paper,corn kernels were selected as the research object due to their high cracking rate dried by hot air.In order to accurately model the changes of drying stress and predict the formation of stress cracks in corn kernels during hot air drying.Firstly,the edge contour and size parameters of corn kernel were extracted by image processing technology and used to reconstruct its three-dimensional geometric model.Then,the information of temperature,moisture and stress in corn kernels was obtained by the stress mathematical model coupled with the heat-mass transfer.Finally,the stress cracking characteristics of corn grain were predicted by comparing their von Mises stress with yield stress.The results showed that:1)The moisture content and temperature data determined by the hot air drying experiments were good agreement with the results simulated by the heat and mass transfer mathematical model with the maximum deviation 7.28% and 9.64% respectively,which indicated that the drying model can be used to further explore the changes of temperature and moisture in corn kernels during hot air drying.2)The simulated results showed that the temperature gradient and moisture gradient in the outer layer of corn kernels were larger than those in the inner layer during drying.The same distribution trend was also found for the wet stress,thermal stress and total stress.The aver

关 键 词：干燥 应力 模型 玉米籽粒 湿热传递 水分梯度 应力裂纹 

分 类 号：TS255[轻工技术与工程—农产品加工及贮藏工程] TQ028[轻工技术与工程—食品科学与工程]