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how to specify inlet species?

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Old   November 27, 2018, 11:16
Default how to specify inlet species?
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Hello, im new to cfx and i have a volume with 2 inlets and 1 outlet. I have managed to set my inlet velocities and my outlet pressure without problems.

I want to have air coming from one inlet and krypton from the other but i dont seem to find any menu in which i can specify materials or species for my inlets. thanks a lot for the help
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Old   November 27, 2018, 18:20
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I assume the air and krypton are both gases which mix. If this is correct then a multicomponent model is the appropriate physical model for this. And once you have set this up as a multicomponent model you can set the mass fraction of the material entering at each inlet, so one inlet can be air and one inlet can be krypton.
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Old   November 28, 2018, 04:26
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1 Under domain settings, you can add more materials (air, krypton) both as gas
2 Under inlet boundary condition settings you must specify the mass fractions of gasses, and under initialization settings you have to add the values
(air=1 krypton=0) would mean 100% air
or (air=0,75 krypron=0,25) would mean 75% air
like here: https://cfd.ninja/multi-species/

I usually make an expression for the other material
so the sum of these two numbers is always 1.
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Old   November 28, 2018, 10:07
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thanks a lot for the help, the tutorial helped a lot the changes to domain settings and defining a material mixture did the trick. i set one inlet as mass fraction air: 1.0 krypton 0.0 and the other as mass fraction air: 0.0 and krypton: 1.0.

Can i initialize the domain with both krypton and air set to 0.0 or should i give some kind of starting value? i dont really expect both gases to mix all that well with the domain having krypton rich >0.99 and air rich regions. so i dont know which would be better between a full krypton or a full air initialization. is it okay to initialize with bot air and krypton set to 0.0?
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Old   November 28, 2018, 11:54
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If you are doing a steady state simulation initial gues will not matter much as the domain will be flushed anyway.
I vould initialize the mass fractions vith what you think the end result will be if the mass flow for both gasses is the same I would put 0.5,0.5.
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Old   November 28, 2018, 13:53
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ok, i will initialize it with air then

thanks a lot
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Old   November 29, 2018, 04:32
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In these cases I strongly recommend to put monitor points in the corners of your geometry where you monitor the fractions of the components. By creating plots in the solver manager, you can follow the development of the fractions during the calculation . Your solution will be (close to) converged if the fractions become constant. This might take longer than you think!
Also, monitor the global balances. Meaning that the amount of krypton entering your domain equals the amount that leaves the domain.
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