# Simulation CFD

#### Gas volume

198 Views, 6 Replies
01/13/2018 2:55 PM

Hello , it's me again ! I hope you're doing well and that you're having a nice weekend.

Let's me explain the situation. As we can see in the  photo We have a cover and a bottom . The gas ( CO2 ) , goes through the inlet then goes up throught the hole in the cover. The whole thing is surrounded by air so I added an external volume and used the scalar mixing methode. I want to see is if the CO2 is covering the whole purple area before going out through the outlet.

So I have two questions . The first is about the fluid volume that is representing the gas. Should I creat a volume just in the tubes in the bottom area and see what the CO2 is going to do after ? or Should I creat a volume in both the cover and the bottom part . My second question is that before going through the tubes the gas was supposed to be moist. In the boundary conditions , I just assigned a humidity to the inlet and didn't do anything to the material.

That is all , thank you in advance.

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#### Re: Gas volume

01/15/2018 12:09 PM

Nice to have you back on the forum!

I will answer what I can but I am not clear what you are trying to do.

1. Where is the fluid? just in the grey parts of the drawing?

2. Where will the Co2 mix with air?

As a general point you must have volumes created for all fluid regions.

For now I would worry only about getting the flow and mixing results before thinking about adding humidity (but for future reference when you want to analyse humidity the density variation method for the gas should be set to "Moist Gas").

All the best,

David

David Short
Technical Support Specialist, Simulation
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#### Re: Gas volume

01/16/2018 7:52 PM

Hello,

The fluid ( CO2) is in the grey part of the model. what I'm doing is varying the diameter of the hole in the upper part of the cover , to see where the two gases mix for every case

The first is with D = 60 mm and the second is D= 45 mm . Red is Co2 ( Scalar = 1 ) and the blue is air ( scalar =0)

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#### Re: Gas volume

01/17/2018 8:56 AM

Please can you send an .cfz file?

Thanks,

David

David Short
Technical Support Specialist, Simulation
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#### Re: Gas volume

01/17/2018 5:08 PM

Hello ,

you can find the file attached to this post !

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#### Re: Gas volume

01/18/2018 10:00 AM

After looking at your model I have a few points:

1. You cannot have internal BCs therefore if you want to use the external air volume, only apply BCs to the exterior surfaces of this volume.

2. You may only need to model the internal fluid space (plus an extension on the outlet) as I cannot see how the external air will effect the flow in the device.

3. Are you sure the flow is compressible? run incompressible with Mach number result quantity enabled and then check to see if the flow is really compressible.

4. I would leave humidty for now. Don't add to much complexity at the beginning. Start simple and get something running first. Also with this setup combining scalar and humidty is probably not possible as you can only select one density variation method but density would be varying with both scalar and humidity here.

Hope that helps a little,

David

David Short
Technical Support Specialist, Simulation
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