About gas dispersion in closed space

Edwin_lee · May 6, 2024, 08:30

Hello guys !
I want to simulate how carbon-monoxide flows into the room through a nozzle and how it spreads over time as shown in the photo.
So my problem is that I want to model like in the attached photo, and I don't know how to set the boundary conditions that will allow CO to spread throughout the indoor space. I want to simulate like example2 picture. Could you please give me some help?

Gerry Kan · Yesterday, 03:13

Dear Edwin:

How are you introducing the CO? I assume you are (literally) setting up two species (air and CO; O2, N2, CO; or something similar). If that is the case you need to introduce thermodynamic properties of each species involved (i.e., viscosity, density, and heat capacity). This information might be available (or, or a first test, set them all to air properties). The caveat is, each component now has a transport equation you need to deal with, which adds to computational effort.

What you can do, is to introduce CO as a tracer (passive scalar). At the inlet you can assign its fraction to 1 (or to whatever volumetric fraction prescribed in your problem). The value of this scalar in the domain will eventually be your molar fraction, just like the figures your presented. CO (30) is about the same molecular weight as air (28.8). While it will eventually sink to the bottom of the chamber, it probably won't happen for the time of dispersion you are considering.

While you could still model your chamber explicitly as an air / CO problem and use the corresponding thermodynamic properties, I don't think you are going to see drastically different results than, say, if you just treat CO as a tracer.

Hope that helps, Gerry.

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Yesterday, 03:13		#2
Gerry Kan Senior Member Gerry Kan Join Date: May 2016 Posts: 350 Rep Power: 10	Dear Edwin: How are you introducing the CO? I assume you are (literally) setting up two species (air and CO; O2, N2, CO; or something similar). If that is the case you need to introduce thermodynamic properties of each species involved (i.e., viscosity, density, and heat capacity). This information might be available (or, or a first test, set them all to air properties). The caveat is, each component now has a transport equation you need to deal with, which adds to computational effort. What you can do, is to introduce CO as a tracer (passive scalar). At the inlet you can assign its fraction to 1 (or to whatever volumetric fraction prescribed in your problem). The value of this scalar in the domain will eventually be your molar fraction, just like the figures your presented. CO (30) is about the same molecular weight as air (28.8). While it will eventually sink to the bottom of the chamber, it probably won't happen for the time of dispersion you are considering. While you could still model your chamber explicitly as an air / CO problem and use the corresponding thermodynamic properties, I don't think you are going to see drastically different results than, say, if you just treat CO as a tracer. Hope that helps, Gerry.