Simulation And Experimental Research On Heat Mass Transfer Process Of Sandy Soil Porous Media

With the improvement of the national economy, the problem of agricultural production and environmental governance have been paid great attention by people, the solution of these problems is inseparable from the research on heat mass transfer process of sandy soil porous media. At present, the traditional models have not adequately considered the effect of soil physical structure, which is assumed to be a continuous medium. In the research of soil heat mass transfer process, these models can neither really reflect the internal porous media complex topology, nor explain some phenomena such as advantage flow phenomenon reasonably. In view of the above problems, this paper take the sand bed as a typical representative, and the pore network theory is applied to the heat and mass transfer of soil porous medium. The following aspects were carried out to analyze these issues:First, the mesh extraction and mesh regularization of sandy soil in real life was conducted, and the pore network physical model of sandy soil porous medium was built. The most common five structural parameters for describing physical model are presented, which are distribution law, distance between two nodes, the space distribution coefficient, model size number and the coordination number. These parameters were correspond to the characteristic parameters of the sandy soil porous media, which are porosity, particle size distribution, pore size distribution and pore coordination number. Then, the pore network theory can be applied to the actual theoretical analysis of heat and mass transfer in the sandy soil porous media.On the basis of the established physical model, the mechanism of heat and mass transfer process is analyzed and the basic assumption for the establishment of mathematical model were made. Then, the pore network mathematical model of the sandy soil porous medium was constructed. The heat and mass transfer process control equation was built and the boundary conditions and initial conditions for the different external environment(sun, wind, rain) were given. The mathematical model was solved by the finite element method. Program development and Simulation of the established model was conducted by applying the combination of VC++and Matlab programming language.With Sand bed as experiment materials, the heat and mass transfer process of sand bed under different atmospheric conditions (sun, wind and rain) was simulated by using self-made test equipment. The structure parameters of the sand bed were determined, and the average moisture content distribution curves and temperature distribution curves were obtained through experimental results. In order to make a comparison between the pore network model and continuous media model, the traditional continuity assumption method for continuous model is established, and then the moisture content distribution curve and the temperature distribution curve were obtained through simulation analysis with ANSYS.By comparing the simulation results with the experimental results, it is concluded that the model can effectively describe the process of heat and mass transfer in sandy soil porous media. With the conditions of the wind and the sun, the initial stage for wet saturated soil, moisture gradient is small, capillary force is small, and soil moisture content change slowly, with the change of time, the capillary force increases gradually, and the change of moisture content gradually speed up. Solar radiation influence on soil temperature is quiet bigger. With the conditions of the rain, the initial phase of soil is dry saturated state, infiltration caused by gravity makes moisture content change quickly, with the change of time, the capillary force gradually increased, and the change of moisture content tended to be slow. The influence of different structural parameters of material is that the greater the porosity and the number of coordination number, the faster the drying rate and the reduction of the coordination number resulted in the generation of the wet mass.