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UDF-Mass Fraction

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Old   July 26, 2018, 13:41
Default UDF-Mass Fraction
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I have a cube and this cube has two zones. The first is a very small zone and is just a constant source term of a gas (Kg/m^3 s) while the other one is porous and initially is filled with air. There is some sort of absorption within the porous media of that gas and not for the air. In Fluent, the solid particles in the porous media are imaginary. I would like to account for this absorption as a UDF sink term to be hooked in the transport equation of that gas. My question is, how can I get the mass fraction of the gas in the volume of voids and not in the imaginary solid volume? The problem is Fluent consider the entire porous volume as fluid and does not consider the porosity for the gas fraction.

My sink term is in Kg/m^3 s (dC/dt = f(time); represents the rate of change or the absorption). I wrote a UDF with DEFINE_EXECUTE_AT_END and within it, I put a condition if the mass fraction of the gas multiplied by the density (kg/m^3) is higher than dC = f(time )*dt (the amount to be absorbed) then the sink term is valid otherwise is equal to zero. Then a DEFINE_SOURCE for the sink term.

I was told that the sources in porous need to be scaled by the porosity function but I do not understand what does this mean. And how can I get the correct mass fraction?

Other question, from the mass fraction, is there a way to get kg/m^3 s) out of this mass fraction in the UDF?

Please help! Than you,
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mass fraction, porous, udf

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