# how to specify inlet species?

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 November 27, 2018, 10:16 how to specify inlet species? #1 New Member   Join Date: Oct 2018 Posts: 8 Rep Power: 7 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

 November 27, 2018, 17:20 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,732 Rep Power: 143 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. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 November 28, 2018, 03:26 #3 Senior Member   urosgrivc Join Date: Dec 2015 Location: Slovenija Posts: 365 Rep Power: 11 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.

 November 28, 2018, 09:07 #4 New Member   Join Date: Oct 2018 Posts: 8 Rep Power: 7 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?

 November 28, 2018, 10:54 #5 Senior Member   urosgrivc Join Date: Dec 2015 Location: Slovenija Posts: 365 Rep Power: 11 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.

 November 28, 2018, 12:53 #6 New Member   Join Date: Oct 2018 Posts: 8 Rep Power: 7 ok, i will initialize it with air then thanks a lot

 November 29, 2018, 03:32 #7 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,836 Rep Power: 27 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. urosgrivc likes this.

 Tags cfx, inlet, material, materials, species