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 Glenn Price March 21, 2000 19:53

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?

 Sung-Eun Kim March 21, 2000 20:24

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.

 Greg Perkins March 23, 2000 00:58

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.

 Dr. Yazid Bindar April 27, 2000 06:17

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

 Rüdiger Schwarze June 27, 2000 11:37

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 Sung-Eun Kim. The results coincide qualitatively with experimentel data from tracer tests.