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Diffusion through porous media. HELP!!

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Old   April 22, 2014, 22:03
Default Diffusion through porous media. HELP!!
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Hami Asma'i
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Hello,

I am modelling a situation which urea need to pass through soil. My geoetry is just like a quadrant of urea at the edge of a box. I need expert's opinion on what model should I use (Multiphase or Species Transport).

Currently, I am using Species Transport which looks more promising. I am now wondering where in FLUENT I actually can set the diffusion coefficient.

Meanwhile, for the soil region, I just set it as a porous zone. But the problem I face is for the velocity resistance formulation. I can't find any way yet to set the direction as radial.

I hope any experts out there can assist me to figure out how to get this thing down. Thank you in advance.
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Old   April 23, 2014, 13:47
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@ hamiasmai
In your geometry modeler, you must define the soil zone as fluid. Then, in Fluent, you need to define it as porous zone. After you defined the appropriate porous zone, then you can adjust the porous zone by setting porosity, viscose resistance (inverse of permeability), inertial coefficient and even more. The good point is that you can set the values for each of them in in-plane or through plane. For diffusivity, you can set it easily in mass diffusivity (several options exist there) in material panel or you can define it by employing user-defined function (UDF). There is a predefined macro for it in Fluent I hope it helps
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Old   April 23, 2014, 22:58
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@A CFD free user

First of all, thanks for your reply and concern.

I understood most of your suggestion such as to set the porous zone and done it actually. But I am not clear of what you said as quoted below.

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@ hamiasmai
The good point is that you can set the values for each of them in in-plane or through plane.
By the way, are you saying that I am already in the right track using Species model?
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Old   April 24, 2014, 14:41
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Quote:
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@A CFD free user

First of all, thanks for your reply and concern.

I understood most of your suggestion such as to set the porous zone and done it actually. But I am not clear of what you said as quoted below.



By the way, are you saying that I am already in the right track using Species model?
Thanks for the positive words,
I meant that you can model anisotropic properties in porous zone as well. In cases that the value of a property for instance, viscose resistance in a particular direction (x, y, z) is less or more than others, the anisotropic model is employed. Have a look at anisotropic properties in Fluent and you can learn more. If you think that the permeability or other properties in your model is different in the directions, here, you can model it using anisotropic diffusivity. For anisotropic, again, you can set it by values in directions or you can use anisotropic diffusivity macro to define it. Regarding the second question, I suppose, the species model or prescribing a user-defined scalar (UDS) will work out in your case. I hope it helps
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