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why does fluent use species mass fraction as default inlet condition?

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Old   May 11, 2020, 10:19
Default why does fluent use species mass fraction as default inlet condition?
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hi all,

I am trying to set species inlet condition of a combustor according to fuel equivalence ratio mentioned in the paper.

I am wondering why does fluent use mass fraction as default inlet condition instead of mole fraction?

Because it would be more convenient to use mole fraction of species to set equivalence ratio of fuels.

Best regards

Weiqiang
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Old   May 11, 2020, 10:43
Default Mole Fractions
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Fluent provides option to use mole fraction instead of mass fraction; if you are using old version then it will only have mass fraction. It's primarily for legacy reason but also because primary users of Fluent in the industry do not use mole fractions but mass fractions.
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Old   May 11, 2020, 21:48
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Quote:
Originally Posted by vinerm View Post
Fluent provides option to use mole fraction instead of mass fraction; if you are using old version then it will only have mass fraction. It's primarily for legacy reason but also because primary users of Fluent in the industry do not use mole fractions but mass fractions.
Hi Vinerm,

Thanks very much for your answer!

Best regards

Weiqiang
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Old   May 12, 2020, 04:14
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The governing equations for the species transport equation are written in mass fraction. Since that's the primitive variable that the solver operates on, naturally it should default to mass fraction.


It's way easier to build transport equations this way valid for compressible flows because the advective flux is the mass-flux.
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Old   May 12, 2020, 04:24
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Quote:
Originally Posted by LuckyTran View Post
The governing equations for the species transport equation are written in mass fraction. Since that's the primitive variable that the solver operates on, naturally it should default to mass fraction.


It's way easier to build transport equations this way valid for compressible flows because the advective flux is the mass-flux.
yes, thanks very much for your answer. it enlightened me a lot.

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Weiqiang
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