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Old   May 24, 2005, 10:29
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stu
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What is the meaning of :- porous media???
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Old   May 24, 2005, 12:08
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Steve
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Think of a sponge
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Old   May 25, 2005, 03:10
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stu
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what is sponge ??? am not an english native speaker-SORRY!
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Old   May 25, 2005, 04:13
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Steve
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A porous medium is something that allows fluid to flow through it. Media is the plural of medium.
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Old   May 25, 2005, 05:34
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stu
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Perfect, do you think gas-liquid is a porous media, what about three-phase such as gas-liquid-oil then!!!!
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Old   May 25, 2005, 05:48
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Harry Fulmer
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no, porous media is usually a solid that allows fluid (gas or liquid) to pass 'through' or 'between' it.
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Old   May 25, 2005, 09:21
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Jim_Park
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Think of water (or oil) seeping through a bed of sand. Or air flowing through a filter.
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Old   May 25, 2005, 11:05
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stu
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This is what I want Jim, thank you.

The question now is: how can one develop a mathematical model?

Can we think of the two-phase flow model, two-fluid model, which suffer from too many mathematical problems as we know???? Or what about considering the relative velocity between the two phases to consider a mixture model, forget about the ill-posedness for the meantime.

Any ideas then!!!!!!
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Old   May 25, 2005, 13:17
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Jim_Park
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Depends on the details of course.

Often with the flow of a fluid in sand (small pores), you can model the flow using Darcy's law, which is essentially

velocity = - (k/rho) grad p. (1)

k is the permeability, which in the stuff I worked with was determined experimentally. Rho is the fluid density of course, and p is the pressure.

This essentially replaces the momentum equations. For incompressible, take the divergence of eq. (1) and you have a continuity statement,

div (v) = - div {(k/rho) [grap p]} = 0 (2)

Looks a lot like a LaPlace equation, doesn't it? The equation gets a bit more complex if you consider compressible flows and/or unsteady flows.

I haven't tried to weave this into an established CFD code - it always seemed to be easier to just code it up. The boundary conditions are usually on the normal component of velocity. So you use eq. (1) to get a pressure gradient on the boundary from those boundary conditions.

For situations where the Darcy assumptions don't work, take a look at a two-phase formulation of the NS equations and set one phase velocity to zero. That might (?) work in a commercial CFD code with a two-phase capability.

Good luck!
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Old   May 27, 2005, 00:30
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yazid
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could u please described that what u mean two-phase formulation of the NS equations and set one phase velocity to zero. That might (?) work in a commercial CFD code with a two-phase capability.

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Old   May 27, 2005, 08:41
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Jim_Park
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It'll be hard to write that out on this web site.

You might want to look at Bird, Stewart, and Lightfoot, "Transport Phenomena", a classic chemical engineering text (been around for more than 50 years but periodically updated). Look at the chapters outlined in the right-hand column of table 1.

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