Research on the effect of surface roughness on gas diffusion coefficient of porous media embedded with a fractal-like tree network

Gas diffusion in fractal pores does not follow the classic Fick’s and Knudsen’s laws, so more research on gas diffusion in fractal porous media is needed. Fractal pore models are generated using the random walk method. The gas diffusion governing equations for the fractal pores are derived from the classic kineti theory of gases. The gas diffusion model is used to study the gas diffusion in fractal porous meida and to determine steady-state diffusion coefficient formulas. The results show that the diffusion coefficient is proportional to the mean proe diameter, porosity, and the exponetial function of the fractal dimension in the Knudsen diffusion regime. The diffusion coefficient is not only related to the three pore parameters but is also related to the molecular mean free path in the configurational diffusion regime.

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Mathematical Model for Effective Gas Diffusion Coefficient in Multi-scale Fractal Porous Media

E3S Web of Conferences ◽

10.1051/e3sconf/202124801026 ◽

2021 ◽

Vol 248 ◽

pp. 01026

Author(s):

Du Zhehua

Keyword(s):

Mathematical Model ◽

Porous Media ◽

Diffusion Coefficient ◽

Fractal Dimension ◽

Fractal Theory ◽

Effective Diffusion ◽

Gas Diffusion ◽

Pore Connectivity ◽

Multi Scale ◽

Pore Area

Based on the capillary hypothesis and fractal theory, a mathematical model for calculating the effective gas diffusion coefficient in porous media is established. By using fractal geometry theory, pore area fractal dimension, tortuosity fractal dimension and pore connectivity are introduced to quantitatively characterize the real internal structure in the porous media. An effective gas diffusion coefficient model for the fractal porous media is derived, and the influence of multi-scale porous media microstructure parameters on the effective gas diffusion coefficient is discussed. The results show that effective gas diffusion coefficient approximates to linearly increase with the increase of porosity, the pore area fractal dimension and the effective gas diffusion coefficient is positive correlation, but the tortuosity fractal dimension is negatively related to it. In the case of different porosities, the gas effective diffusion coefficient varies with the change of the pore diameter ratio, the effective gas diffusion coefficient increases with the increase of pore connectivity.

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A time dependent model to study the effect of surface roughness on reactive–diffusive transport in porous media

Journal of Nuclear Materials ◽

10.1016/j.jnucmat.2009.01.168 ◽

2009 ◽

Vol 390-391 ◽

pp. 203-206 ◽

Cited By ~ 8

Author(s):

M. Warrier ◽

A. Rai ◽

R. Schneider

Keyword(s):

Surface Roughness ◽

Porous Media ◽

Time Dependent ◽

Diffusive Transport ◽

Transport In Porous Media ◽

Dependent Model ◽

Time Dependent Model ◽

Effect Of Surface

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Measurement of Oxygen Diffusion Characteristics of Porous Media Used for the Gas Diffusion Layer of Proton-Exchange Membrane Fuel Cells

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 2 ◽

10.1115/ht2007-32604 ◽

2007 ◽

Author(s):

Shixue Wang ◽

Yoshio Utaka ◽

Yutaka Tasaki

Keyword(s):

Porous Media ◽

Diffusion Coefficient ◽

Experimental Method ◽

Diffusion Layer ◽

Oxygen Diffusion ◽

Proton Exchange Membrane ◽

Gas Diffusion Layer ◽

Gas Diffusion ◽

Proton Exchange ◽

Exchange Membrane

It is known that the mass transfer characteristics of the gas diffusion layer (GDL) are closely related to the performance of a proton-exchange membrane fuel cell. In this study, an experimental method was established for measuring the gas diffusion coefficient in porous media by using an oxygen concentration sensor based on a galvanic battery operating at normal temperature. The oxygen diffusion coefficient in air measured by this method corresponded with data in the literature within ±6% deviation. The oxygen diffusion coefficients of two kinds of porous media generally used for the GDL were measured by the experimental method for dry and wet samples. The results indicate that the gas diffusion coefficient in porous media not only depends on porosity but is also affected by other factors, for example, tortuosity. It was also found that the diffusion coefficient in different directions, for example, through-plane and in-plane, in porous media can be very different. The oxygen diffusion coefficient in the porous media containing liquid water varied nonlinearly with the saturation level and was strongly affected by other factors as well.

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FRACTAL MODEL OF GAS DIFFUSION IN FRACTURED POROUS MEDIA

Fractals ◽

10.1142/s0218348x18500354 ◽

2018 ◽

Vol 26 (03) ◽

pp. 1850035 ◽

Cited By ~ 4

Author(s):

QIAN ZHENG ◽

JINTU FAN ◽

XIANGPENG LI ◽

SHIFANG WANG

Keyword(s):

Porous Media ◽

Diffusion Coefficient ◽

Fractal Dimension ◽

Gas Transport ◽

Fractal Model ◽

Gas Diffusion ◽

Diameter Ratio ◽

Fractured Porous Media ◽

Length Ratio ◽

Branching Angle

Understanding gas transport behavior though fractured porous media is essential in many fields including fiber science, energy science, soil science, environmental engineering, chemical engineering, etc. In this paper, a fractal model is developed to characterize gas diffusion through fractured porous media, where a bundle of fractal-like tree branching networks is used to represent the fracture system according to fractal scaling laws. The analytical expression for relative gas diffusion coefficient of fractured porous media is derived. The proposed fractal model has been validated by the available experimental data and empirical correlations. From the parametrical study, it can be seen that structural parameters of fractured porous media (for example porosity, the fractal dimension, the diameter ratio, the length ratio and the branching angle) have a significant effect on equivalent gas transport properties. Gas relative diffusion coefficient has a positive correlation with the porosity, the pore size fractal dimension, or the diameter ratio, whereas it has a negative correlation with the length ratio, the branching levels, or the branching angle. The proposed fractal model does not only shed light on gas transport physics of fractured porous media, but also reveals more mechanisms than experimental measurements.

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