I want to know the steady concentration of a specie after it is injected from chimney into air,I think it isn't possible to define multiple species,but i don't know how to define material and operating condition,especially how to define the diffusivity of that specie,which I think is the most important parameter in diffusion.And from the caculation,I can only know the velocity of the mass instead of the concentration of it,what is the matter,is diffusion equation included in FLUENT? How can I see it? thank you for your help.

Hi there,

Not sure if u hv found the answer to ur question, but thot I'll juz give u my 2cents worth of opinion all the same.

Your problem is rather similar to mine. u hv to define the 2 materials. one, is air, and the other is the emmision from the chimney. U can then define multiple species by going to 'species' and enabling the multiple species button. After which, go back to the material panel and add in the above 2 materials.Define the properties of the mixture consisting of air and emmission. U can define ur diffusivity coefficient there. U can also input in an equation. For me, I use a constant diffusivity of 1e-08 (fluid), for gases, I would think it is in the range of 1e-5. U have to verify it.

Hope it is helpful.

Cheers JJ

thank you very much.But why the solution is only resulted from convection diffusion instead of molecular diffusion.I want to know the mass concentration of the specie by both convection diffusion and molecular diffusion, how can I do with it? thank you again.

Hi, I'm not too sure I udst ur question. However, I would like to know how u verify that the diffusion was attributed to convection and not molecular? May I ask what is the difference in temp of the emmission from air? or the density difference?

JJ