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permeability coefficients

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Old   August 25, 2004, 10:18
Default permeability coefficients
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CMB
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Hi, if the porous medium I use is very thin and the change in pressure across it is negligible, how can I calculate the permeability coefficients? Neither the methodology volume nor the user guide says anything about changing normal units of permeability [m^2 or m^2/s] to [kg/(m^3 s)]. Would appreciate any help on this. Many thanks, CM
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Old   August 28, 2004, 20:09
Default Re: permeability coefficients
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R
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CM, If the change in pressure across the very thin porous medium is negligible, then personally I would not use a porous media. What is it that you are trying to calculate? I have used this feature as an "artifical" way to raise the pressure drop across a relatively thin medium. It is best to use test data if available to determine what your coefficients should be...otherwise it is difficult to be accurate. -R
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Old   August 30, 2004, 11:06
Default Re: permeability coefficients
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CMB
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Hi, I am more interested in the limited diffusion of the species of a gas mixture, rather than in the pressure drop across the porous medium. I am talking about a 0.3 mm thick porous layer, similar to those used in some electrochemical cells. I do have some experimental data, I know the permeability in normal units [cm^2] and the porosity.
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Old   August 30, 2004, 15:40
Default Re: permeability coefficients
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R
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Is your medium more like a screen or a fiber/felt? I am not familiar with electrochemical cell layers, but maybe you have very little restriction in the flow direction and heavy restriction in the other 2 axial directions.? If that is true, then see example 2 in the methodology manual (v3.10). The important part being that the alpha and beta for the flow direction would be low and the alphas and betas for the other 2 directions would be very high. (This is where your experimental flow data comes in.) I do not think calculating alphas and betas would be the way to go. Determining them experimentally is much better. -Good luck, R.
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