Study On Percolation And Drying Of Porous Media By Using Fractal Theory

Heat and mass transfer inside porous media has spread in industrial and agricultural production and in many fields of human society life. In particular, modeling and simulation about the percolation and the drying moisture migration process inside porous media has been a center and challenging problem. However, it's a quite difficult job to set up a model which can properly describe transfer processes inside porous media because of the complex inner structure of porous media. The theories based on the hypothesis of a continuous porous body are constrained, and the regular pore network model doesn't realistically describe the complex inner structure of porous media. Fractal theory would offer new ideas and methods on transfer processes inside porous media. At present, the research on this area is still in its beginning stage. The study describes the complex inner structure of porous media using fractal theory in order to simulate the percolation and the drying moisture migration process.Taking into account the structural complexity in the study of transport phenomena in porous media, the expressions of porosity and permeability are derived using fractal theory and knowledge of fluid mechanics in the paper. And the predicted permeability values are analyzed by comparing with the available empirical formulas Ergun equation, and compared with those of experimental measurements to verify this model. The physical and mathematical models about level pipe full of porous media are set up and calculated based on SIMPLE algorithm in order to gain effects of the complex inner structure of porous media on percolation process.The study describes the drying moisture migration process using fractal theory and knowledge of transfer process. Firstly, diffusion process inside porous media is analyzed, and a fractal pore network model is set up based on fractal dimension and pore surface fractal dimension. And effects of dimensions on diffusion process are obtained on this model. On this basis, the equations of liquid evaporation and gas phase diffusion are discretized. Then, air convection drying of potato is simulated on fractal pore network model in order to gain effects of various temperatures, hot air rates, et al on drying process. At last, effects of model parameters on drying characteristics are researched by simulation, which characterize quantitatively effects of irregular pore structure inside pore media on drying process.The analytical and simulative results obtained in this work will be greatly valuable and significant for the understanding of the percolation and the drying moisture migration process inside porous media.