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-   -   Is it possible to model a packed bed (http://www.cfd-online.com/Forums/fluent/30089-possible-model-packed-bed.html)

 Jomba July 29, 2002 14:08

Is it possible to model a packed bed

Hi

any one already tried or modeled a packed bed? please give me a hint on it

Jomba

 Jin-Wook LEE July 29, 2002 22:48

Re: Is it possible to model a packed bed

Many and many previous studies for the packed bed have been done and are being done by using 'porous media' approach.

Sincerely, Jinwook

 Erwin July 30, 2002 07:41

Re: Is it possible to model a packed bed

Yeah, but the 'porous media' approach only means that Fluent takes care of the extra momentum losses in a packed bed. For the rest it's a bit too simple; even though you specify porosity (for energy equation) the actual velocity is taken as superficial velocity. Also, none of the available turbulence models (pretty important if you need to model thermal or species dispersion) is suitable for a dense medium like a packed bed. The effective conductivity is a simple mass weighted average of solid and fluid, this is normally a bit more complex than that. But the Fluent model does account for thermal inertia.

 Jomba July 30, 2002 17:26

Re: Is it possible to model a packed bed

thanx Jin and Erwin for the assistance. But my system is in turbulent region and ivlove thermal and species dispersion too, should I include UDF to enhance the Fluent turbulent model or it is impossible ..??

 Shankar July 30, 2002 17:52

Re: Is it possible to model a packed bed

Hi Erwin

Superficial velocity is the volumetric flow rate/cross-sectional area, right?Can you give a more 'physical' explanation of what superficial velocity actually means?

Thanks. Shankar.

 Erwin July 31, 2002 03:43

Re: Is it possible to model a packed bed

Well, the superficial velocity is the velocity as if there is no packed bed. The actual velocity is therefore higher, namely v_act = v_sup / porosity.

The literature contains several suggestions for a fixed bed turbulence model, I have no idea how difficult it will be to implement them in a UDF.

It may be more important to fix the effective bed thermal conductivity, I calculated two examples yesterday where the Fluent approach gives a value that is 10 - 20 times too high...

 Joern July 31, 2002 04:04

Re: Is it possible to model a packed bed

With some simplifications it should be possible to modell a packed bed directly.

If you assume a regular structure of speres with the same size it is possible to create only a fraction of the mesh using the symmetrie of the packing. With some mirroring and copying it is easy to create a larger part of the mesh.

If so you should be able to use any of the cfd-codes for the calculation.

This kind of calculation was presented at a (european) starcd users meeting some years ago. Maybe the people from computational dynamics can send you the article.

 Shankar July 31, 2002 12:06

Re: Is it possible to model a packed bed

So actual velocity is the velocity with the presence of packed bed and shouldnt it be lesser because of the resistance offered by the packed bed? Is there any alternative to "porous medium" model for modeling packed bed in Fluent.Thanks. Shankar.

 Greg Perkins August 8, 2002 03:56

Re: Is it possible to model a packed bed

For most problems this approach is not practical and thus a lumped model is used. However, this approach is useful to aid in establishing good correlations for the heat and mass transfer, dispersion and turbulence that can be used in a lumped parameter model.

Greg

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