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Old   August 26, 2014, 11:45
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zahra
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Hi everyone,
I am using chtMultiRegionFoam in openFoam 2.0.1 my model has 4 parts inclouding 3 solid parts(glass, fiberglass (as insolation) , aluminum) and 1 fluid(air) part.
in constant folder of solid parts we can see a solidThermophysicalProperties which have a radiation properties section similar to the following:
//- radiation properties
kappa kappa [0 -1 0 0 0 0 0] 0;
sigmaS sigmaS [0 -1 0 0 0 0 0] 0;
emissivity emissivity [0 0 0 0 0 0 0] .88;

first question: as i have read sigmaS is Scatter coefficient [1/m] and kappa is Absorption coefficient [1/m]. is it true? what are these coefficients? absorption coefficient for solids should not be dimensionless? does scattering have any meaning for solids?


second question: what are the values of absorption and emission coefficient for air in ordinary temperature?

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Old   August 26, 2014, 14:33
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Himanshu Sharma
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Quote:
Originally Posted by zahraa View Post
Hi everyone,
I am using chtMultiRegionFoam in openFoam 2.0.1 my model has 4 parts inclouding 3 solid parts(glass, fiberglass (as insolation) , aluminum) and 1 fluid(air) part.
in constant folder of solid parts we can see a solidThermophysicalProperties which have a radiation properties section similar to the following:
//- radiation properties
kappa kappa [0 -1 0 0 0 0 0] 0;
sigmaS sigmaS [0 -1 0 0 0 0 0] 0;
emissivity emissivity [0 0 0 0 0 0 0] .88;

first question: as i have read sigmaS is Scatter coefficient [1/m] and kappa is Absorption coefficient [1/m]. is it true? what are these coefficients? absorption coefficient for solids should not be dimensionless? does scattering have any meaning for solids?


second question: what are the values of absorption and emission coefficient for air in ordinary temperature?


Hi,

Here is a very good link to understand the details of Radiation modelling from chalmers university.
I hope it can be helpful to you.
http://www.tfd.chalmers.se/~hani/kur...Foam_final.pdf
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Old   August 27, 2014, 02:26
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Hi,
Thank you for the link , I had read it yesterday , before I made this thread, unfortunately it didn't answer my questions
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Old   August 28, 2014, 07:10
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it is interesting, nobody knows!
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Old   August 28, 2014, 08:48
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Absorption coefficient is a kind of decay length, hence the unit.

I don't know the absorption coefficient for air at room temperature, sorry.
Keep in mind that in reality the absorption coefficient is a function of the frequency.
In the case of a grey radiation model the absorption coefficient is spectrally averaged.

I don't know much about the scattering coefficient, I don't use it for gases. It might be useful if the gases contain particles, maybe in flame simulation?
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