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UDS for Porous Media

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Old   September 5, 2003, 19:13
Default UDS for Porous Media
  #1
cp
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Hi All,

I am using UDF to model the solid temperature distribution in a heated porous media, through which cold air passes through. My domain is 8" long and the porous media is 1" thick and kept at 5" from the inlet. Currently, I have defined a UDS for solid temperature. It is by default applied throughout the domain, whereas the porous media is for only 1". How do I modify the UDS, which can be applied to only the specific section in the domain? What changes do I need to make in my UDF?

Any information on this would be helpful,

Thanks in advance,

Chendhil.
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Old   September 6, 2003, 02:16
Default Re: UDS for Porous Media
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Greg Perkins
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You'll have to be careful with this to make sure you are in fact modelling the two phases correctly.

My advice is to consider NOT using the porous media model for this situation but rather just use the standard gas phase and your UDS. To understand why, consider (for example) how you intend to model thermal conductivity in your "porous zone" and your "uds". You'll have to modify the normal conductivities to make adjustment for the fact that your porous zone is not really porous now just the gas phase etc. It can be done, but you'll have to work through that. I suggest you write down your equations exactly and then formulate whatever models you use to recover those equations exactly.

I've put some code for FLUENT 5.X a number of years ago (2000 I think) for doing the UDS stuff and interphase heat transfer in the udf code library and you may find it by searching the posts. That should give you a start, but the code needs some minor mods for FLUENT 6.x

Greg
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Old   September 6, 2003, 18:16
Default Re: UDS for Porous Media
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cp
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Thanks a lott Greg, for your valuable information.

I've got your code "udf_scalar_dos.c" from the repository and am looking into it. I will get back to you after understanding your implementation. I may have some questions. Hope you don't mind helping me out with this!!

Chendhil.
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Old   September 7, 2003, 19:10
Default Re: UDS for Porous Media - To Greg
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cp
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Hi

I looked at your code, "udf_scalar_dos.c". That was really an excellent code, well-written and with several self-explanations. Good! Now, I have a question: With reference to my posting on handling the porous media at a specified location in the domain, I think you have done it this way. Please correct me, if I am wrong.

1. You bypass all Fluent's in-built porous models and calculate the momentum source (based on the problem in hand)

2. Initialize the porosity in the actual porous region and set 1 in other places. I guess, this is where you handle the specific location of porous media in your domain.

3. Calculate the UDS solid diffusivity

4. Calculate solid-phase/fluid phase energy source terms with current porosity

5. Solve for Solid Temp, leaving ZETA intact

It would be helpful to me, if you explain any missing points. Thanks,

Chendhil.
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Old   September 7, 2003, 19:27
Default Re: UDS for Porous Media - To Greg
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Greg Perkins
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I don't have the code handy at the moment, but from memory that's sounds right.

Yes I don't use any internal FLUENT models. The only problem with this comes if you want to handle unsteady problems in which case the gas phase transient term will be incorrect by a factor of the porosity.

Zeta represents the bed/porous media porosity - I think its constant for this early version, but you can also solve a UDS for that so it changes with say reaction. These features are in my later codes and aren't in the basic one I posted.

Also, I think that basic code assumes a constant specific heat for the solid. In wish case I have divided it through the equation. For variable specific heat this needs to be modified.

Greg
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Old   September 8, 2003, 10:38
Default Re: UDS for Porous Media
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cp
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Thanks a lott for your information, Greg!!

Chendhil.
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Old   June 26, 2012, 13:44
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Piyush Sharma
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Hi,
I am also working on the porous media and need to solve it for solid temperature, it will be of great help if you could send me the "udf_scalar_dos.c", although i tried to find out but could not succeed in locating the file.

Thanks in Advance

Piyush Sharma
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