How to account for diffusion?

offroader10052 · August 28, 2023, 01:47

Need a short explanation
what are the enable settings in ansys CFX,
take into account diffusion between gases,
so that not 2 continuums move,
and the mutual deepening of the media was taken into account.

An example of a task in the photo.

offroader10052 · August 28, 2023, 02:27

I send the supplemented scheme in English

offroader10052 · August 28, 2023, 02:29

Sorry, the picture is rotated vertically again

ghorrocks · August 28, 2023, 04:41

I assume the CH4 and air are a gas. In this case this looks like a multicomponent mixture model. You set up a gas mixture of CH4 and air as a variable composition material and use this as the fluid for the domain. You have to define mass fractions at the inlets and a diffusion coefficient. I think this covers all the physics you need.

Note that gravity will not have any effect on the mixture composition, in other words the air and CH4 will not separate due to gravity. The mixture can rise due to buoyancy, but not separate.

August 28, 2023, 04:41		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,712 Rep Power: 143	I assume the CH4 and air are a gas. In this case this looks like a multicomponent mixture model. You set up a gas mixture of CH4 and air as a variable composition material and use this as the fluid for the domain. You have to define mass fractions at the inlets and a diffusion coefficient. I think this covers all the physics you need. Note that gravity will not have any effect on the mixture composition, in other words the air and CH4 will not separate due to gravity. The mixture can rise due to buoyancy, but not separate. Opaque and offroader10052 like this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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August 28, 2023, 02:29		#3
offroader10052 New Member Ilya Join Date: Oct 2019 Posts: 16 Rep Power: 6	Sorry, the picture is rotated vertically again