Study Of Some Transport Properties For Gas Flow And Diffusion Through Fractal Porous Media

In nature and engineering applications, gas flow and diffusion through porous media have received more and more extensive attention. It has been shown that most of porous media have fractal characters, such as random, disordered, self-similar properties. So we can employ the fractal geometry theory to characterize complex porous systems, and then study gas transport properties. At first, this dessertation briefly introduces porous media and outlines the structural parameters of the proposed models composed of a bundle of capillaries and fractal-like tree branching network, respectively. Then, this work summarizes regionalism and transport features (for gas permeability and diffusion coefficient) of gas flowing and diffusing in porous media.In Chapter 2, the fractal geometry analytical method is used to study the problems of gas flow through porous media. Fist, the model of a bundle of capillaries is applied to characterize porous media. Then we build a theoretical model for gas slippage factor in the slip flow regime, and analyze the variation of gas slippage factor versus intrinsic/liquid permeability and structural parameters of porous media. After that, we use the fractal-like tree network to simulate fissured network and use a bundle of capillaries to describe the matrix medium. A theoretically predictive model for permeability of gas flow through dual-porosity porous media is derived. It is found that the model predictions are in good agreement with available experimental data and simulations. The proposed gas permeability is expressed as a function of structural features of porous media and has no empirical constant. Thus, this model can reveal more physical mechanisms than empirical models. Finally, a model for gas leakage rates through contact surfaces under non-isothermal condition is built. This model is not only related to the structural paprameters, but it is also related to temperature. The proposed model can be applied to study the gas leakage rate through closed container.In Chapter 3, the fractal geometry theory is used to study the problem of gas diffusion through porous media. If pores/channels in porous media have not or weak connection, we use the model, a bundle of tortuous capillaries, to characterize porous media. If pores/channels in porous media interact each other, the model that matrix is embedded with a fractal-like tree network is used to characterize porous media. Then, the theoretical models for diffusion coefficients for gas diffusing through the two types of porous media, i.e. models consisting of a bundle of capillaries and matrix embedded with the fractal-like tree network, are developed. The model predictions are in good agreement with available experimental data. In addition, the effects of parameters of porous media on gas diffusivity are also analyzed.In Chapter 4, the test particle Monte Carlo method is applied to simulate the gas transmission probability in complex channels (a single chamber-throat pore and angular changeable cylindrical elbow). Geometrical model of channel is firstly constructed, and then the effects of structural parameters of channels on gas transmission probability are studied.Finally, the conclusions and innovations of the present thesis are presented, and some comments are also made on the potential research subjects and directions about gas transports in porous media in future.