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-   -   Porosity PPI : how convert in % ? (http://www.cfd-online.com/Forums/fluent/86659-porosity-ppi-how-convert.html)

 Rich1979 March 29, 2011 10:39

Porosity PPI : how convert in % ?

Hi all,
i have a question about modeling a porous media.
I have as information for my porous media its PPI , pores per inch(40 or 50 foe ex.).
Fluent input for porosity is instead in % (fluid volume/media volume).
How could i convert ppi to percentage?
Thanks mates :)

 samuraiufrn February 15, 2012 11:03

You must have at least two of these four informations: porosity, mean pore diameter, mean particle diameter and pore density. You can relate mean pore diameter and mean particle diameter with the expression:

Dpore=4*(Dparticle*porosity)/[6*(1-porosity)]

If you already have the mean particle diameter value, you can use this expression directly:

Poredensity (ppcm)=(300/Dparticle)*sqrt[(1-porosity)^2/(porosity*pi)]

All diameters given in meters. It's easy to deduce these expressions if you consider one particle for each pore and consider the porous media as arranjed spheres. Another hint is if you have the permeability (K) value and mean particle diameter, so using Ergun's expression, you got:

K=(porosity^3*Dpart^2)/[b*(1-porosity)]

Where b=144 for most porous cases.

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