土壤多孔介质热质传递过程数值模拟与试验研究

发布时间：2018-01-20 08:27

  本文关键词： 土壤 多孔介质 传热传质 孔道网络 模拟与试验　出处：《陕西科技大学》2016年硕士论文　论文类型：学位论文

【摘要】：随着国民经济的提高,农业生产和环境治理问题受到了人们的高度重视,这些问题的解决都离不开对土壤多孔介质热质传递过程的研究。目前所建立的传统模型没有充分考虑土壤物理结构的影响,将其假设为连续性介质考虑。在研究土壤热质传输过程中,不能真实反映多孔介质内部复杂的拓扑结构,也不能合理解释一些现象如优势流等。针对以上问题本论文以砂土为典型代表,将孔道网络理论引用到土壤多孔介质热质传递的研究领域,进行了以下研究：首先运用孔道网络理论对现实生活的中砂土堆进行了网格提取并将网格规则化处理,构建了土壤多孔介质孔道网络物理模型。对物理模型中常用的五个结构参数：分布律、孔隙节点间距、空问分布系数、模型规模数以及配位数进行描述,并将这些参数与土壤多孔介质的特征参数：孔隙率、粒径分布、孔径分布以及孔隙配位数进行了一一对应,使孔道网络理论可以应用于实际土壤多孔介质热质传递的理论分析中。在物理模型的基础上,对热质传递过程机理进行了分析,并对所建模型作了基本假设。构建了土壤多孔介质孔道网络数学模型,建立了质量、热量传递过程控制方程,并给出了不同外界环境下(风吹、日晒、雨淋)的边界条件和初始条件。运用有限元法对所建立的数学模型进行了求解。采用VC++与Matlab语言联合编程对所建立的模型进行程序开发及模拟。以砂土床为试验物料,使用自制的试验装置模拟了不同大气环境条件(日晒、风吹、雨淋)下砂土床热质传递过程。确定了砂土床的各个结构参数,并通过试验得到了砂土床的平均湿含量分布曲线、温度分布曲线。为与孔道网络模型进行对比,采用传统连续性假设方法建立了连续性模型并采用ANSYS进行模拟分析,得到了湿分场和温度的变化曲线。通过模拟结果与试验结果的对比分析可以得出,所建立的模型能够较好的描述实际土壤多孔介质的传热传质过程。风吹和日晒时,初始阶段土壤为湿饱和状态,水分梯度较小,导致毛细力较小,从而土壤湿含量变化较慢,随着时间的推移,毛细力逐渐增大,湿含量变化逐渐加快。砂土温度受太阳辐射影响较大；雨淋时,初始阶段土壤为干饱和状态,重力作用引起的下渗使湿含量变化较快,随着时间的推移,毛细力逐渐增大,湿含量变化趋于缓慢。多孔介质的不同结构参数对热质传递过程的影响为孔隙率、配位数越大则干燥速率越快,配位数减小导致了湿团现象的产生。
[Abstract]:With the improvement of national economy, people attach great importance to the problems of agricultural production and environmental management. The solution of these problems is inseparable from the study of the heat and mass transfer process in porous soil media. The traditional models established at present do not fully consider the influence of soil physical structure. In the study of soil heat and mass transport, the complex topological structure of porous media can not be truly reflected. Some phenomena such as dominant flow can not be explained reasonably. Aiming at the above problems, this paper applies the theory of pore network to the research field of heat and mass transfer in porous soil. The following studies are carried out: firstly, the mesh extraction and regularization of the meshes are carried out by using the theory of pore network. In this paper, the physical model of porous soil pore network is constructed, and the five structural parameters commonly used in the physical model are described: distribution law, pore node spacing, spatial distribution coefficient, model size and coordination number. These parameters are correlated with the characteristic parameters of soil porous media, such as porosity, particle size distribution, pore size distribution and pore coordination number. The theory of pore network can be applied to the theoretical analysis of heat and mass transfer in soil porous media. Based on the physical model, the mechanism of heat and mass transfer is analyzed. The mathematical model of porous soil pore network was constructed, the control equations of mass and heat transfer were established, and the different external environment (wind and sun) were given. Rain). The finite element method is used to solve the established mathematical model. VC is used to solve the problem. The model was programmed and simulated with Matlab language. The sand bed was used as the test material. The heat and mass transfer process of sand bed under different atmospheric conditions (sun, wind, rain) was simulated by using self-made test device. The structure parameters of sand bed were determined. The average wet content distribution curve and temperature distribution curve of sand bed are obtained by experiments, which are compared with the pore network model. The continuity model is established by using the traditional continuity hypothesis method and simulated by ANSYS. The variation curves of the wet field and the temperature are obtained, which can be obtained by comparing the simulation results with the experimental results. The model can well describe the heat and mass transfer process of the actual soil porous media. When the wind and sunlight, the initial phase of the soil is wet saturated state, the water gradient is small, resulting in a small capillary force. As a result, soil moisture content changes slowly, with time, capillary force gradually increases, moisture content change gradually accelerate, sand temperature is greatly affected by solar radiation; In the initial stage of rain, the soil is dry saturated, the infiltration caused by gravity makes the moisture content change faster, and the capillary force increases gradually with the passage of time. The effect of different structure parameters of porous media on the heat and mass transfer process is porosity. The larger the coordination number is, the faster the drying rate is, and the smaller the coordination number is, the wet mass is produced.
【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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本文编号：1447541