[nyko21]

Hi, I'm really new to the ANSYS CFX and I got a problem. I need to simulate flow of 2 gases (NO2 and CO2) through the membrane, one gas should go through, and the other one should stop by the membrane (retentate) and go for the outlet. I got simple pipe with 3 components: first one is the smallest pipe, when i have inlet and let in my mixture, then i got 1 ring pipe which is membrane and then the biggest ring which is my permeate. Can anyone help what empirical reactions should i use for my permeate and retentate. I got inlet data, and im really struggling how to define my membrane and volume fractions value at the outlet for retentate and for permeate.

[Gert-Jan]

What exact question do you want to solve when performing this simulation?
And what reaction is taking place?

[nyko21]

I need to check how much of a mixture will be stopped by the membrane (retentate) and what will be separated through the membrane (permeate). Its just laminare flow of the mixture without heat exchange.
This is my geometry : https://ibb.co/cYMCT7m
The smallest pipe is where I insert my mixture with outlet for the retentate on the other side. Next is the first ring which is my porous membrane, and the second ring pipe is my permeate zone.
If it possible i can try to solve this simulation with just Air, but i don't now if it make sense to try separate 1 fluid through the membrane

[Gert-Jan]

In CFX your membrane is just an empty box. You need to feed it with properties/model to let the permeate go through and leave the retentate behind.
What do you have in mind for this? There is no membrane model in CFX that you can pick from the shelf. There are no adsorption models or what so ever.
You can model the membrane as a porous volume, to match your pressure drop, but separation is not included.

[nyko21]

In setup I have add a new material, and describe it as porous domain with all properties that i need. But my problem is that I don't know how to set correct equations of CO2 for both sides, permeat outlet and retentate leftovers.

[Gert-Jan]

1) In Materials, you have to define a mixture of both components.
2) In Domain, set one of the components as contraint

2) Set the incoming mass fraction of the other component at the inlet
3) let it run.

[nyko21]

Thanks, I will try this option. Should i left 0.0 mass fraction at the retentate and permate outlets for component that i define at inlet?

[Gert-Jan]

you don't prescribe the massfractions at the outlet. That should be an outcome of your simulation.

[nyko21]

Yes I know, but the default is set to 0.0 i cant choose any other option than massfraction for this. In domain I set CO2 Ideal Gas as Cointrant just like you said and N2 Ideal Gas I set as Transport Equations but for both Outlets there is no CO2 and on N2 there is only Mass Fraction option set default to 0.0

Screenshot of what I mean: https://ibb.co/YXHGTHZ

edit: My bad, I got selected Opening instead of Outlet.

[Gert-Jan]

Indeed. Use Outlet instead of opening.
Also, please don't add pictures via link.
Better add pictures directly in this forum via the menu "Go Advanced", at the bottom of your reply window.

[ghorrocks]

Just checking: Are you using a multicomponent mixture for this, or a multiphase model?

[nyko21]

At first I tried to use multicomponent mixture, but I can't make it work at all, so now I will try to create new mixture made of those two gases like Gert-Jan suggested.

[ghorrocks]

They are completely different physical models and are not interchangeable. You definitely should not be choosing the physical model just because your first attempt at using it did not work.

If the materials are mixed such that it is all a single phase and diffusion controls the motion then you need multicomponent mixture. If the mixture is separable phases (liquid/gas, continuous/droplets, continuous/bubbles) then you need a multiphase model.