A FRACTAL MODEL FOR PREDICTING OXYGEN EFFECTIVE DIFFUSIVITY OF POROUS MEDIA WITH ROUGH SURFACES UNDER DRY AND WET CONDITIONS

Fractals ◽  
2021 ◽  
pp. 2150076
Author(s):  
BOQI XIAO ◽  
QIWEN HUANG ◽  
BOMING YU ◽  
GONGBO LONG ◽  
HANXIN CHEN
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Oxygen Diffusion ◽  
Water Saturation ◽  
Rough Surfaces ◽  
Effective Diffusivity ◽  
Fractal Model ◽  
Relative Roughness ◽  
Oxygen Diffusivity ◽  
Dry And Wet Conditions

Oxygen diffusion in porous media (ODPM) with rough surfaces (RS) under dry and wet conditions is of great interest. In this work, a novel fractal model for the oxygen effective diffusivity of porous media with RS under dry and wet conditions is proposed. The proposed fractal model is expressed in terms of relative roughness, the water saturation, fractal dimension for tortuosity of tortuous capillaries, fractal dimension for pores, and porosity. It is observed that the normalized oxygen diffusivity decreases with increasing relative roughness and fractal dimension for capillary tortuosity. It is found that the normalized oxygen diffusivity increases with porosity and fractal dimension for pore area. Besides, it is seen that that the normalized oxygen diffusivity under wet condition decreases with increasing water saturation. The determined normalized oxygen diffusivity is in good agreement with experimental data and existing models reported in the literature. With the proposed analytical fractal model, the physical mechanisms of oxygen diffusion through porous media with RS under dry and wet conditions are better elucidated. Every parameter in the proposed fractal model has clear physical meaning, with no empirical constant.

A FRACTAL MODEL FOR KOZENY–CARMAN CONSTANT AND DIMENSIONLESS PERMEABILITY OF FIBROUS POROUS MEDIA WITH ROUGHENED SURFACES

Fractals ◽  
2019 ◽  
Vol 27 (07) ◽  
pp. 1950116 ◽  
Author(s):  
BOQI XIAO ◽  
YIDAN ZHANG ◽  
YAN WANG ◽  
GUOPING JIANG ◽  
MINGCHAO LIANG ◽  
...  
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Fluid Transport ◽  
Fractal Theory ◽  
Fractal Model ◽  
Physical Mechanisms ◽  
Relative Roughness ◽  
Fibrous Porous Media ◽  
Effect Of Surface ◽  
Good Agreement

In this paper, fluid transport through fibrous porous media is studied by the fractal theory with a focus on the effect of surface roughness of capillaries. A fractal model for Kozeny–Carman (KC) constant and dimensionless permeability of fibrous porous media with roughened surfaces is derived. The determined KC constant and dimensionless permeability of fibrous porous media with roughened surfaces are in good agreement with available experimental data and existing models reported in the literature. It is found that the KC constant of fibrous porous media with roughened surfaces increases with the increase of relative roughness, porosity, area fractal dimension of pore and tortuosity fractal dimension, respectively. Besides, it is seen that the dimensionless permeability of fibrous porous media with roughened surfaces decreases with increasing relative roughness and tortuosity fractal dimension. However, it is observed that the dimensionless permeability of fibrous porous media with roughened surfaces increases with porosity. With the proposed fractal model, the physical mechanisms of fluids transport through fibrous porous media are better elucidated.

Microporous Layer Consisting of Alternating Porous Material With Different Wettability for Controlling Moisture in Gas Diffusion Layer of PEFC

2010 ◽  
Author(s):  
Yoshio Utaka ◽  
Ikunori Hirose
Keyword(s):  
Porous Media ◽  
Porous Material ◽  
Diffusion Layer ◽  
Oxygen Diffusion ◽  
Water Saturation ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Single Type ◽  
Oxygen Diffusivity ◽  
Diffusion Characteristics

The oxygen transfer characteristics of the gas diffusion layer are closely related to the cell performance of a polymer electrolyte fuel cell. In this study, a new hybrid gas diffusion layer is proposed in which two porous media with different wettabilities are arranged alternately for augmentation of the oxygen diffusivity in the gas diffusion layer. Since the movement of water from hydrophobic to hydrophilic media due to the difference in capillary pressure, the oxygen diffusion paths in the porous media can be maintained. The oxygen diffusion characteristics with respect to water saturation were measured using an experimental apparatus that uses a galvanic battery oxygen sensor as an oxygen absorber. The experimental results demonstrate that the hybrid structure has superior oxygen diffusion characteristics than a conventional gas diffusion layer with a single porous material with moisture. That is, the effective oxygen diffusivity of the hybrid configuration was almost five times larger than that of the single type at water saturation S = 0.2.

A physically based model for the electrical conductivity of partially saturated porous media

2020 ◽  
Vol 223 (2) ◽  
pp. 993-1006
Author(s):  
Luong Duy Thanh ◽  
Damien Jougnot ◽  
Phan Van Do ◽  
Nguyen Van Nghia A ◽  
Vu Phi Tuyen ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Porous Media ◽  
Fractal Dimension ◽  
Water Saturation ◽  
Theoretical Models ◽  
Fluid Composition ◽  
Physically Based Model ◽  
Partially Saturated ◽  
Proposed Model ◽  
Physically Based

SUMMARY In reservoir and environmental studies, the geological material characterization is often done by measuring its electrical conductivity. Its main interest is due to its sensitivity to physical properties of porous media (i.e. structure, water content, or fluid composition). Its quantitative use therefore depends on the efficiency of the theoretical models to link them. In this study, we develop a new physically based model that takes into account the surface conductivity for estimating electrical conductivity of porous media under partially saturated conditions. The proposed model is expressed in terms of electrical conductivity of the pore fluid, water saturation, critical water saturation and microstructural parameters such as the minimum and maximum pore/capillary radii, the pore fractal dimension, the tortuosity fractal dimension and the porosity. Factors influencing the electrical conductivity in porous media are also analysed. From the proposed model, we obtain an expression for the relative electrical conductivity that is consistent with other models in literature. The model predictions are successfully compared with published experimental data for different types of porous media. The new physically based model for electrical conductivity opens up new possibilities to characterize porous media under partially saturated conditions with geoelectrical and electromagnetic techniques.

Fractal Model for Thermal Conductivity of Wetting, Fibrous Porous Media

2012 ◽  
Vol 496 ◽  
pp. 12-16
Author(s):  
Fang Long Zhu ◽  
De Hong Xia ◽  
Yu Zhou
Keyword(s):  
Thermal Conductivity ◽  
Porous Media ◽  
Fractal Dimension ◽  
Effective Thermal Conductivity ◽  
Fractal Model ◽  
Self Similarity ◽  
Conductivity Model ◽  
Electrical Analogy ◽  
Fibrous Porous Media ◽  
Thermal Conductivity Model

The current paper deals with the fractal effective thermal conductivity model for fibrous porous media containing unsaturated water moisture. The model is based on the thermal-electrical analogy and statistical self-similarity of porous media. The fractal effective thermal conductivity model can be expressed as a function of the pore structure (fractal dimension) and architectural parameters of porous media. It is expected that the model will be helpful in the evaluation of thermal comfort for textiles in the whole range of porosity.

Oxygen Diffusion Characteristics of Gas Diffusion Layers With Moisture

2008 ◽  
Author(s):  
Daigo Iwasaki ◽  
Yoshio Utaka ◽  
Yutaka Tasaki ◽  
Shixue Wang
Keyword(s):  
Porous Media ◽  
Liquid Water ◽  
Oxygen Diffusion ◽  
Gas Diffusion ◽  
Vacuum Impregnation ◽  
Impregnation Method ◽  
Moist Air ◽  
Oxygen Diffusivity ◽  
Diffusion Characteristics ◽  
Experimental Apparatus

The mass transfer characteristics of the gas diffusion layer (GDL) in a polymer electrolyte fuel cell (PEFC) are closely related to the performance. In this study, the oxygen diffusivity of paper and cloth type porous media, which are generally used as GDLs, were measured with respect to liquid water content, using experimental apparatus consisting of an oxygen sensor based on a galvanic battery. Paper type porous media, both non treated and hydrophilic treated, and the cloth type porous media with non treated surface were used as GDL specimens. The porosity of both specimens was almost the same, but the representative pore diameter of the cloth type GDL was approximately three times larger than that of paper type GDL. Two methods were utilized to impregnate liquid water into the porous GDL media to realize different water distributions in the specimens at the initial state; vacuum impregnation and moist air condensation impregnation. The oxygen diffusivities of the specimens were measured to clarify the influence of the two impregnation methods on the oxygen diffusion characteristics. Moreover, the relation between the measurement of oxygen diffusivity and the visualization of the liquid water distribution by using Neutron Radiography [Tasaki et al. (2007)] was investigated for the paper and cloth type GDLs. The oxygen diffusivity in the paper type porous media decreased precipitously with increasing water saturation by the vacuum impregnation method, whereas the diffusivity decrease was relatively small when impregnated by the moist air condensation method. For the cloth type porous media with weaving threads, oxygen diffusion characteristics were independent of the water impregnation method. Thus, the porous medium’s microstructure plays an important role in determining diffusion characteristics, especially in the presence of liquid water.

A NEW RELATIVE PERMEABILITY MODEL OF UNSATURATED POROUS MEDIA BASED ON FRACTAL THEORY

Fractals ◽  
2020 ◽  
Vol 28 (01) ◽  
pp. 2050002
Author(s):  
KE CHEN ◽  
HE CHEN ◽  
PENG XU
Keyword(s):  
Experimental Data ◽  
Porous Media ◽  
Fractal Dimension ◽  
Multiphase Flow ◽  
Relative Permeability ◽  
Volume Fraction ◽  
Fractal Model ◽  
Accurate Estimation ◽  
Unsaturated Porous Media ◽  
Flow Through

The multiphase flow through unsaturated porous media and accurate estimation of relative permeability are significant for oil and gas reservoir, grounder water resource and chemical engineering, etc. A new fractal model is developed for the multiphase flow through unsaturated porous media, where multiscale pore structure is characterized by fractal scaling law and the trapped water in the pores is taken into account. And the analytical expression for relative permeability is derived accordingly. The relationships between the relative permeability and capillary head as well as saturation are determined. The proposed model is validated by comparison with 14 sets of experimental data, which indicates that the fractal model agrees well with experimental data. It has been found that the proposed fractal model shows evident advantages compared with BC-B model and VG-M model, especially for the porous media with fine content and texture. Further calculations show that water permeability decreases as the fractal dimension increases under fixed saturation because the cumulative volume fraction of small pores increases with the increment of the fractal dimension. The present fractal model for the relative permeability may be helpful to understand the multiphase flow through unsaturated porous media.

A DIFFUSIVITY MODEL FOR GAS DIFFUSION IN DRY POROUS MEDIA COMPOSED OF CONVERGING–DIVERGING CAPILLARIES

Fractals ◽  
2016 ◽  
Vol 24 (03) ◽  
pp. 1650034 ◽  
Author(s):  
SHIFANG WANG ◽  
TAO WU ◽  
YONGJU DENG ◽  
QIUSHA ZHENG ◽  
QIAN ZHENG
Keyword(s):  
Experimental Data ◽  
Porous Media ◽  
Fractal Dimension ◽  
Fractal Theory ◽  
Knudsen Diffusion ◽  
Fractal Model ◽  
Gas Diffusion ◽  
Pore Area ◽  
Relative Diffusivity ◽  
Fluctuation Amplitude

Gas diffusion in dry porous media has been a hot topic in several areas of technology for many years. In this paper, a diffusivity model for gas diffusion in dry porous media is developed based on fractal theory and Fick’s law, which incorporates the effects of converging–diverging pores and tortuous characteristics of capillaries as well as Knudsen diffusion. The effective gas diffusivity model is expressed as a function of the fluctuation amplitude of the capillary cross-section size variations, the porosity, the pore area fractal dimension and the tortuosity fractal dimension. The results show that the relative diffusivity decreases with the increase of the fluctuation amplitude and increases with the increase of pore area fractal dimension. To verify the validity of the present model, the relative diffusivity from the proposed fractal model is compared with the existing experimental data as well as two available models of Bruggeman and Shou. Our proposed diffusivity model with pore converging–diverging effect included is in good agreement with reported experimental data.

TORTUOSITY–POROSITY RELATIONSHIP IN TWO-DIMENSIONAL FRACTAL MODEL OF POROUS MEDIA

Fractals ◽  
2013 ◽  
Vol 21 (02) ◽  
pp. 1350013 ◽  
Author(s):  
SELLY FERANIE ◽  
FOURIER D. E. LATIEF
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Lattice Gas ◽  
Empirical Relation ◽  
Fractal Model ◽  
Flow Equation ◽  
Two Dimensional ◽  
Porous Substance ◽  
Numerical Result ◽  
Random Algorithm

Tortuosity (τ) of two-dimensional fractal model of porous media is investigated to study their relationship with porosity. Square full-walk technique is applied to obtain τ in a two-dimensional fractal model of porous substance constructed by Randomized Sierspinski Carpets. The numerical result is in good agreement with previous results and empirical relation between tortuosity and porosity given by τ ~ p(1 - ϕ) + 1 that was found by other using Lattice Gas Automata method for solving flow equation on two-dimensional porous substance constructed by randomly placed rectangles of equal size and with unrestricted overlap. Average tortuosity of the flow path decreases linearly as fractal dimension of pore increases at each fractal iteration. Both fractal dimension and iteration give almost the same linearly tortuosity–porosity relation. The type of random algorithm for constructing Randomized Sierspinski Carpets has no significant influence on the tortuosity–porosity relation.

scholarly journals A Numerical Study on Gas Flow through Anisotropic Sierpinski Carpet with Slippage Effect

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Shuxia Qiu ◽  
Lipei Zhang ◽  
Zhenhua Tian ◽  
Zhouting Jiang ◽  
Mo Yang ◽  
...  
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Gas Flow ◽  
Gas Permeability ◽  
Fractal Model ◽  
Numerical Results ◽  
Pore Scale ◽  
Gas Slippage ◽  
Slippage Effect ◽  
Flow Through

A pore-scale model has been developed to study the gas flow through multiscale porous media based on a two-dimensional self-similar Sierpinski carpet. The permeability tensor with slippage effect is proposed, and the effects of complex configurations on gas permeability have been discussed. The present fractal model has been validated by comparison with theoretical models and available experimental data. The numerical results show that the flow field and permeability of the anisotropic Sierpinski model are different from that of the isotropic model, and the anisotropy of porous media can enhance gas permeability. The gas permeability of porous media increases with the increment of porosity, while it decreases with increased pore fractal dimension under fixed porosity. Furthermore, the gas slippage effect strengthens as the pore fractal dimension decreases. However, the relationship between the gas slippage effect and porosity is a nonmonotonic decreasing function because reduced pore size and enhanced flow resistance may be simultaneously involved with decreasing porosity. The proposed pore-scale fractal model can present insights on characterizing complex and multiscale structures of porous media and understanding gas flow mechanisms. The numerical results may provide useful guidelines for the applications of porous materials in oil and gas engineering, hydraulic engineering, chemical engineering, thermal power engineering, food engineering, etc.

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