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-   -   Use of DO radiation with multiphase model (http://www.cfd-online.com/Forums/fluent/92235-use-do-radiation-multiphase-model.html)

yashmash September 7, 2011 06:46

Use of DO radiation with multiphase model
 
Hi guys,

I am using the DO radiation model together with mixture model to simulate UV radiation within a slurry reactor. The radiation model requires the input of the material's absorption coefficient. This works when I have a constant absorption coefficient for the wavelength range investigated.
However, when I use a non gray model (4 wavelength bands) for which the absorption coefficient varies with the wavelength and if I input a different value for each band (gray band tab in materials section), it seems that those values are not taken into consideration and that fluent returns a result for which the absorption coeffcient is zero within the mixture.
Can someone tell me why this is happening??
Your assistance is very much appreciated :)

Nikolopoulos September 16, 2011 10:38

Quote:

Originally Posted by yashmash (Post 323258)
Hi guys,

I am using the DO radiation model together with mixture model to simulate UV radiation within a slurry reactor. The radiation model requires the input of the material's absorption coefficient. This works when I have a constant absorption coefficient for the wavelength range investigated.
However, when I use a non gray model (4 wavelength bands) for which the absorption coefficient varies with the wavelength and if I input a different value for each band (gray band tab in materials section), it seems that those values are not taken into consideration and that fluent returns a result for which the absorption coeffcient is zero within the mixture.
Can someone tell me why this is happening??
Your assistance is very much appreciated :)

I'm not sure what's the answer in your problem but I have some experience with radiation models.
I think that they cannot be applied in multiphase flows. I ' ve seen the UDFs for P1 (UDS) and it is problematic for simulations with marticles.

novice September 22, 2011 06:32

Quote:

Originally Posted by yashmash (Post 323258)
Hi guys,

I am using the DO radiation model together with mixture model to simulate UV radiation within a slurry reactor. The radiation model requires the input of the material's absorption coefficient. This works when I have a constant absorption coefficient for the wavelength range investigated.
However, when I use a non gray model (4 wavelength bands) for which the absorption coefficient varies with the wavelength and if I input a different value for each band (gray band tab in materials section), it seems that those values are not taken into consideration and that fluent returns a result for which the absorption coeffcient is zero within the mixture.
Can someone tell me why this is happening??
Your assistance is very much appreciated :)

Hi Yashmash,

did u figure out how u can define the absorption coefficients depending upon different wave lengths?? If so can you please share me some information about it.
I'm also using DO model to simulate irradiation of a lamp at different wavelengths. i came accross the same problem of defining different absorption coeffs at respective wave lengths. If you have some info how to overcome this problem, it will be a real help for me.

Thanks in advance

Novice

yashmash September 22, 2011 23:22

Quote:

Originally Posted by Nikolopoulos (Post 324419)
I'm not sure what's the answer in your problem but I have some experience with radiation models.
I think that they cannot be applied in multiphase flows. I ' ve seen the UDFs for P1 (UDS) and it is problematic for simulations with marticles.

Thanks Nikolopoulos

Yes I have tried the gray band option in the material's absorption coefficient tab as well as a UDF but in both cases the results came back as zero absorption. So it does seem that using different absorption coefficients for different wavelengths in case of multiphase flows is not a possibility at the moment. Thanks for the confirmation,

Yash

yashmash September 22, 2011 23:28

Quote:

Originally Posted by novice (Post 325201)
Hi Yashmash,

did u figure out how u can define the absorption coefficients depending upon different wave lengths?? If so can you please share me some information about it.
I'm also using DO model to simulate irradiation of a lamp at different wavelengths. i came accross the same problem of defining different absorption coeffs at respective wave lengths. If you have some info how to overcome this problem, it will be a real help for me.

Thanks in advance

Novice

Hi,

I suppose that you have already specified your number of bands in the DO model and specified the wavelengths ranges as well. Once you have done this and assuming you are using some kind of gas as your irradiated material, go in material properties and in the absorption coefficient tab, you should have an option that says "gray band". That option allows you to specify an absorption coefficient for each band that you have.
Hope that helps

Yash


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