CO2 concentration simulation

angierain · June 5, 2011, 09:18

Hi everyone, I'd like to simulate the CO2 concentration using CFX for a HVAC system, but I cannot figure out how to define CO2 in CFX-pre. Is there CO2 listed in CFX material library? How to simulate the CO2 concentration in a room with air?
Thanks!

PS: does anyone know how to use Macro Comfort factors?

ghorrocks · June 5, 2011, 19:55

There are simple approaches and complex approaches.

The simple approach is to model the CO2 as an additional variable. In this case you just put a marker in the gas which convects and diffuses with the gas. If the CO2 does not affect the properties of the gas this is a good approach and is very simple to apply.

The complex approach is to use a multi-component fluid, so you model the composition of the gas. This can handle the properties changes as the CO2 concentration changes. It can also handle chemical reactions and other advanced stuff. Only do this approach if the CO2 changes the properties of the gas or if you have chemistry in there as well.

angierain · June 10, 2011, 09:30

Quote:

Originally Posted by ghorrocks

There are simple approaches and complex approaches.

The simple approach is to model the CO2 as an additional variable. In this case you just put a marker in the gas which convects and diffuses with the gas. If the CO2 does not affect the properties of the gas this is a good approach and is very simple to apply.

The complex approach is to use a multi-component fluid, so you model the composition of the gas. This can handle the properties changes as the CO2 concentration changes. It can also handle chemical reactions and other advanced stuff. Only do this approach if the CO2 changes the properties of the gas or if you have chemistry in there as well.

how could i put a marker in the gas? thx!

ghorrocks · June 11, 2011, 08:29

With an additional variable, set to diffusion/convection.

angierain · June 16, 2011, 10:12

Quote:

Originally Posted by ghorrocks

With an additional variable, set to diffusion/convection.

I cannot find how to set to diffusion/convection
You mean set the Option of Addition Variable to Diffusive Transport Equation or Transport Equation?

ghorrocks · June 16, 2011, 19:57

Diffusive transport equation is the one.

spirit-assassin · May 2, 2016, 12:59

i am trying to simulate a person breathing as well. i am a very new used. I have done as you have instructed and added a new variable CO2. the nose was an inlet boundary condition with the 10 mm in diameter and .091 m/s velocity i have set the kinematic diffusion of .091 x 10^-6 no CO2 appears in the results.

evcelica · May 2, 2016, 17:51

And what was the amount of "additional variable" from your inlet? The default would be zero if you didn't change it.

June 5, 2011, 09:18	CO2 concentration simulation	#1
angierain New Member William Shaw Join Date: May 2010 Posts: 18 Rep Power: 16	Hi everyone, I'd like to simulate the CO2 concentration using CFX for a HVAC system, but I cannot figure out how to define CO2 in CFX-pre. Is there CO2 listed in CFX material library? How to simulate the CO2 concentration in a room with air? Thanks! PS: does anyone know how to use Macro Comfort factors?

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June 5, 2011, 19:55		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	There are simple approaches and complex approaches. The simple approach is to model the CO2 as an additional variable. In this case you just put a marker in the gas which convects and diffuses with the gas. If the CO2 does not affect the properties of the gas this is a good approach and is very simple to apply. The complex approach is to use a multi-component fluid, so you model the composition of the gas. This can handle the properties changes as the CO2 concentration changes. It can also handle chemical reactions and other advanced stuff. Only do this approach if the CO2 changes the properties of the gas or if you have chemistry in there as well.

June 11, 2011, 08:29		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	With an additional variable, set to diffusion/convection.

June 16, 2011, 19:57		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,850 Rep Power: 144	Diffusive transport equation is the one.

May 2, 2016, 12:59		#7
spirit-assassin New Member Cairo Join Date: Mar 2016 Posts: 1 Rep Power: 0	i am trying to simulate a person breathing as well. i am a very new used. I have done as you have instructed and added a new variable CO2. the nose was an inlet boundary condition with the 10 mm in diameter and .091 m/s velocity i have set the kinematic diffusion of .091 x 10^-6 no CO2 appears in the results.

May 2, 2016, 17:51		#8
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,186 Rep Power: 23	And what was the amount of "additional variable" from your inlet? The default would be zero if you didn't change it.