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species mass balance not balancing

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Old   December 12, 2016, 16:13
Default species mass balance not balancing
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marc b
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Ok so in all honesty I have just enough experience with Fluent to be dangerous but here goes: I'm modeling a 3-d combusting system (a propane burner) and am trying to see how changes to the burner geometry can affect emissions (really just looking for trends, not absolute numbers, to help inform actual experiments).

As part of this I checked the N2 species balance and I found that there is more N2 leaving my model volume than is entering it (N2 exiting is ~30% higher). I'm using the non-premixed combustion model and the pre-baked Fluent chemistry so N2 should be essentially inert, i.e. I'm not modeling NOx formation so N2_in should equal N2_out...the overall mass balance looks good, fyi. I'm measuring N2 entering/leaving both by the mass-area averaged mass fraction, and just having fluent tell me the flow rate.

Any suggestions on where to start looking for the source of this (apparent) inconsistency (i.e. the mismatch of N2 in vs. out)? I'm hoping that it's something really simple that I'm just missing. The model looks to be converged too. Thanks for any help!
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Old   December 13, 2016, 15:31
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bump...any ideas?
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