Application Of Directional Random Walk Algorithm Based On Fractal Method In The Research Of Heat Transfer In Porous Media

Due to the considerable advantages over ordinary dense materials in thermal insulation, catalytic agent and filtration, porous materials have been widely used in industrial and agricultural production and people’s daily life, which makes deeply research on heat and mass transfer in porous media has extremely important theoretical significance and practical value.Theoretical research on heat and mass transfer in porous media is one of the most important topics in the fields of engineering thermophysics and material science. How to find a way to quantitatively describe the features of internal complicated pore distribution becomes the stumbling block hindering the development of theoretical research. The development of fractal geometry provides a new perspective and method for the research on heat and mass transfer in porous media. The effects of complex structural factors on heat and mass transfer coefficient are mainly studied in our work. The internal porous characteristics are quantitatively described by using fractal geometry and random walk method in this paper. The main contents and achievements are as follows:(1) Analysis of influence of big pores on heat transfer performance. Numerical simulation are adopted to study the effects of shape, arrangement, connectivity and directivity of the macropores on thermal property of porous media. The results show that different shapes with the same porosity and different connective direction with the same shape of macropores would respectively have quite different effects on the thermal conductivity performance of porous media. So it is unreasonable for traditional methods to ignore the effect of shape and aperture distribution on thermal conductivity of porous media.(2) Research on quantitative descriptions of 2-D porous structures and the relevance with thermal performance of porous media. In order to discuss the effects of different pore structures on heat transfer performance, two-dimensional porous media models with the same porosity and different pore structure distribution were made. The model of directional random walk is developed to simulate the real heat transfer process by directional random walk of particle in porous media, the spectral dimension of directional random walk in porous media was calculated and then compared with the effective thermal conductivity. The results show that the spectral dimension of directional random walk has the same trend with the effective thermal conductivity of porous media when porosity are the same.(3) Research on further expandation of directional random walk method. The directional random walk method can also be used to quantitatively describe the pore distribution features of 3-D spatial models. The results show that the distribution of pores have a great influence on heat conduction performance under the conditions of consistant porosity. The directional random walk spectral dimensions calculated by our algorithm mentioned in this paper of these four 3-D porous structure models is coincident with their heat conduction performance.