Question about porous media model
I am about to model the transient flow through a packed bed using FLUENT 5.
As noted in the user manual, the fluid does not accelerate as it moves through the medium because the volume is 100% open and the porosity is not physically represented. Unfortunately, we are interested in the transit time through the bed which is clearly impacted by this limitation. Now for my question, what is the best way to model this situation. One possibility is to reduce the thickness of the bed to yield the correct transit time + adjust the bed parameters to get the correct pressure drop. Any other suggestions? 
Re: Question about porous media model
The reason why many codes, including FLUENT and FIDAP, adopt "filtration" velocity (Q/A)as a dependent variable appears related to the fact that Darcy law after all relates the pressure gradient and the volume flux (Q).
There's a relationship, though, between the "pore" velocity (average over the pore only) and the "filtration" velocity (average over the whole elemental volume including pore and solid) and that is U_pore = U_filtration/porosity. And this could probably be used to estimate the flow transit time, if the porous media is isotropic. 
Re: Question about porous media model
Also according to the addendum to the manual file (fl5_add.ps) versions of Fluent 5.1 or later do include the effect of porosity in the transient term of the porous media equations.

Re: Question about porous media model
What I know that Fluent code models the porous media using Darcy model. However, the flow in porous media range from Viscous dominated regime, Darcy Laminar Regime, Forlzeimer Laminar Regime,..., Turbulence Regime.
Please consider in what regime your flow will be. If it is not in Darcy regime, I think you have to be more critical with the Fluent results. Yazid Bindar 
Re: Question about porous media model
I tried to estimate the residence time of fluid particles in a porous medium in the way suggested by SungEun Kim. The results coincide qualitatively with experimentel data from tracer tests.

Re: Question about porous media model
Hi, Basically fluent models the flow through porous media considering the full momentum equations. Also, fluent accounts for porous media as momentum sink term in the momentum equations. I don't find the effect of porosity felt in the momentum equation except in the source terms. I have quite a lot of literature with modified or reduced form of momentum equations. I am trying to model 2 phase flows in porous media. I would appreciate suggestions regarding this.
Thanks, Madhavan 
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