果蔬多孔介质干燥过程模拟及试验研究

发布时间：2018-04-21 13:25

本文选题：果蔬干燥 + 多孔介质　；参考：《陕西科技大学》2016年硕士论文

【摘要】：近些年来,对于多孔介质干燥的研究越来越受到人们的重视,而采用模型模拟的方法来研究其干燥过程更是研究的热点。由于果蔬多孔介质内部结构十分复杂,而采用传统的连续介质干燥模型模拟的结果与实际果蔬干燥的差距较大,不能较合理的描述多孔介质干燥过程中的传热、传质的规律,而这正好是对于提高果蔬干燥品质的研究所必需的。针对这些问题的研究,本文以苹果为果蔬多孔介质的代表进行其干燥过程的模拟及试验研究：对不规则孔道网络物理模型进行了建立。首先采用实验的方法测定了冻干苹果片的孔隙率、孔隙密度、孔隙直径分布,并确定了孔隙配位数等参数；然后构建了苹果多孔介质的不规则孔道网络物理模型,该模型的参数采用实际测得苹果多孔介质的参数,这样的孔道网络模型模拟能很好地应用于实际苹果多孔介质的干燥过程。以苹果多孔介质为试验对象,进行了苹果片多孔介质的热风干燥试验,试验中对苹果片的温度和湿分含量进行了测量,并得到了其干燥曲线、湿分场、温度曲线和温度场。根据建立的孔道网络物理模型对孔隙尺度上的数学模型进行了建立,包括传热方程、传质方程和能量方程,数学模型将孔隙中的毛细效应及开尔文效应对干燥过程中的传热传质的影响进行了考虑。对所建立的孔道网络物理模型进行了传热、传质网格划分,采用控制容积平衡法对所建立的数学模型进行了差分离散化,进而求解出模型的温度场、湿分场分布。采用VC++和Matlab联合编程软件对苹果片孔道网络干燥进行了模拟分析。通过对模拟结果与试验结果的对比分析可知,所建立的孔道网络模型能够很好的描述实际果蔬多孔介质干燥过程中的热质传递过程,模拟的干燥曲线与实际物料干燥曲线较为接近,模拟的湿分场分布能够反映出实际物料干燥过程中的湿分场分布特征;模拟的温度曲线与实际物料干燥过程中温度曲线的变化趋势基本一致,模拟温度值与试验温度值相比较高。不同的物料结构参数的干燥试验表明：孔隙率、平均配位数等参数对干燥模拟有较大的影响。孔隙率越大,干燥时间就越长,平均温度越低；平均配位数越大,干燥时间就越长,平均温度越高。
[Abstract]:In recent years, more and more attention has been paid to the study of porous media drying. Because the internal structure of porous media is very complex, the result of traditional continuous medium drying model is far from that of actual drying process, so it can not reasonably describe the law of heat and mass transfer in the drying process of porous medium. This is necessary to improve the drying quality of fruits and vegetables. In order to solve these problems, the drying process of apple as the representative of porous medium for fruits and vegetables was simulated and tested. The physical model of irregular pore network was established. The porosity, pore density and pore diameter distribution of freeze-dried apple slices were measured by experimental method, and the parameters of pore coordination number were determined, and then the physical model of irregular pore network in apple porous media was constructed. The parameters of the model are measured by the actual parameters of the porous medium of apple. This model can be used to simulate the drying process of the porous medium of apple. The hot air drying test of apple slice porous media was carried out. The temperature and moisture content of apple slice were measured, and the drying curve, wet field, temperature curve and temperature field were obtained. According to the physical model of pore network, the mathematical model on pore scale is established, including heat transfer equation, mass transfer equation and energy equation. The effects of capillary effect and Kelvin effect on heat and mass transfer during drying are considered in the mathematical model. The physical model of the pore network is divided into heat and mass transfer meshes, and the mathematical model is discretized by using the control volume balance method, and the temperature and moisture distribution of the model is solved. Using VC and Matlab programming software, the drying of apple slice pore network was simulated and analyzed. Through the comparison and analysis of the simulation results and the experimental results, it can be seen that the established pore network model can describe the heat and mass transfer process in the drying process of the actual fruit and vegetable porous media. The simulated drying curve is close to the actual material drying curve, and the simulated wet field distribution can reflect the distribution characteristics of the actual material drying process. The simulated temperature curve is basically consistent with the change trend of the actual material drying process, and the simulated temperature value is higher than the experimental temperature value. The drying test of different material structure parameters shows that the porosity and the average coordination number have great influence on the drying simulation. The larger the porosity, the longer the drying time and the lower the average temperature; the larger the average coordination number, the longer the drying time and the higher the average temperature.
【学位授予单位】：陕西科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK124

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