Study On Fluid Seepage Performance In Fractal Porous Media Based On Random Walk Method

Porous media is a kind of functional material widely distributed in nature,which is composed of solid skeleton and connected pores.The internal pore structure is very complex.Fluid flow and heat transfer in porous media exist in many aspects of industrial production and human life.The random and irregular distribution of micro pore structure make the quantitative characterization of porous media and the study of heat and mass transport properties fail to make breakthrough.Heat and mass transfer in porous media has become the hot and difficult points in many fields of scientific research.Based on the characteristics of the porous media with fractal structure,random walk method is applied in this paper to study the fluid seepage performance in porous media.The characteristics of the pore channel are described using the new random walk model under the driving force of potential difference proposed in this paper.The process and mechanism of mass flow in porous media are numerically simulated.The main achievements of this paper can be summarized as follows:1.Analysis of factors affecting the seepage performance of porous mediaThere are many different types and structures of porous media.Granular porous media are selected to study the seepage performance in this paper.The finite element method is applied to analyze the porosity,the shape,size,arrangement,connectivity and orientation of the particles.The influence of the geometric parameters of the pore(particle)on the percolation performance of porous media is discussed.The results show that the percolation performance of porous media is closely related to the structure of porous media.Because the pore structure has complex and irregular distribution under different conditions,it can not be realized if a large number of geometric parameters are involved in the description of the porous structure,and the simplification of the pore structure is also applicable.The problem of large deviations.Based on the above reasons,the fractal geometry method,which has a unique advantage to describe the complex irregular geometric objects,is used to describe the pore structure in a quantitative way.2.Study on the seepage performance of non-uniform fractal porous mediaBased on fractal theory,a two-dimensional porous media fractal model with the same porosity and different distribution of pore structure and distribution is constructed.The seepage law and influence mechanism of non-uniform self-similar distribution and anisotropy of porous media are analyzed numerically.The results show that the fluid flow in the pore channel has similar characteristics and is consistent with the fractal self-similarity of pore channels.The influence of non-uniform particles on the flow field is different,and the larger the particle is in the flow direction,the greater the influence on the seepage flow.For porous media with similar structure characteristics,the surface integral dimension is the same,and the permeability increases with the increase of porosity.In the same condition,the direction of the long axis of the elliptic particle is perpendicular to the flow direction and the maximum permeability is parallel to the flow direction.The results show that the porosity and the area fractal dimension of the porous media are not enough to fully describe the characteristics of the pore structure.The process and permeability of the percolation are closely related to the structure and distribution of the pore channels.3.Fractal random walk description of pore structure of porous mediaBased on the seepage process in porous media can be seemed as fluid particles flow under the external potential difference,A new directional random walk model is developed to describe the particles walk in porous space of porous media in this paper.Combined with the fractal geometry theory in the concept of spectrum fractal dimension,the conception of directional random walk spectral dimension is putting forward to describe the structure characteristics of pore channel quantitatively.The results show that there is a consistent characteristic between the number of particles in the porous media and the permeability in the pore channels of porous media at the same time.