Abstract
A fractal theory employing a box-counting method was used to describe hydrogen gas diffusion into membrane pores in the meso-porosity regime. The diffusion of the gas into the membrane pore network confirmed the existence of fractal structure in the system. Two fractal identities to represent irregularity and roughness of pore surface and tortuosity of the membrane were obtained and analyzed. Their influences on hydrogen permeability were also evaluated. The fractal permeability model that reflects different hydrogen diffusion mechanisms was calculated and compared with that of the state of the art Kozeny–Carman equation.
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Abbreviations
- Ao :
-
The unit membrane area, cm2
- C:
-
Kozeny–Carman constant defined by Eq. (29)
- De:
-
Effective diffusivity, cm2 s−1
- dE :
-
Euclid dimension
- Df:
-
Area fractal dimension
- dg :
-
Molecular collision diameter of gas, cm
- Dt:
-
Tortuosity fractal dimension
- F:
-
Gas flow through a single pore, cm3 s−1
- К :
-
Permeability, mol cm cm−2 s−1 Pa−1
- kB :
-
Boltzmann constant, 1.38 × 10−23 J K−1
- Kn :
-
Knudsen number
- L:
-
Length scale, cm
- Lo:
-
Representative length of a straight capillary, cm
- ls :
-
Length of the cell space, cm
- M:
-
Mole molecule weight, g mol−1
- N:
-
Number of pores
- n:
-
Kozeny–Carman constant defined by Eq. (28)
- P:
-
Total pressure, Pa
- P:
-
Partial pressure, Pa
- Q:
-
Total gas flow through a membrane, m3 s−1
- R:
-
Gas constant, 8.314 × 107 g cm2 s−2 mol−1 K−1
- T:
-
Temperature, K
- V:
-
Volume, ml g−1
- x:
-
Pore diameter, cm
- f :
-
Loading factor, mol g−1, defined by Eq. (30)
- r or rp :
-
Membrane pore radius, cm defined by Eq. (30)
- rg :
-
Molecular radius of gas species, cm, defined by Eq. (30)
- Δ:
-
Different
- λ:
-
Mean free path, cm
- μ:
-
Viscosity, Pa s
- ρ:
-
Density, g cm−3
- ε:
-
Porosity
- A:
-
Gas A
- K:
-
Knudsen
- m:
-
Mean
- max:
-
Maximum
- min:
-
Minimum
- mn:
-
Membrane
- P:
-
Poiseulle
- p:
-
Pore
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Acknowledgments
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2013R1A2A2A01014540).
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Helwani, Z., Wiheeb, A.D., Shamsudin, I.K. et al. The effects of fractality on hydrogen permeability across meso-porous membrane. Heat Mass Transfer 51, 751–758 (2015). https://doi.org/10.1007/s00231-014-1445-7
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DOI: https://doi.org/10.1007/s00231-014-1445-7