Hi

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

Jomba

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

Sincerely, Jinwook

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.

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 ..??

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.

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...

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.

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.

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