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-   -   Species and reactions (http://www.cfd-online.com/Forums/fluent/30475-species-reactions.html)

Ale November 6, 2002 18:41

Species and reactions
 
Hi,

if you select hydrogen-air as the mixture material, you will see that this mixture includes 9 volumetric species (H2, O2, H2O, O, H, OH, H2O2, HO2, N2), but only 1 global volumetric reaction (H2 + 1/2 O2 ---> H2O).

How can it predict so many species with such a simple kinetics? How does Fluent calculate the source terms for all these species?

Can anybody answer to these questions?

Thanks a lot.

Jin-Wook LEE November 9, 2002 21:31

Re: Species and reactions
 
You can not predict the so many species with such a simple kinetics. Use PDF approach by using prePDF. prePDF is based on the 'fast chemistry'. I think that H2+O2 reaction can be regarded as 'fast chemistry'. Then you can predict many species, upto 20 for current Fluent version.

Sincerely, Jinwook


Ale November 11, 2002 17:28

Re: Species and reactions
 
Thank you Jinwook for your answer. I know that with such a simple kinetics I cannot predict so many species, that's what makes me surprised.

If you enable Species Transport in Fluent 6, you can choose the hydrogen-air mixture, and see that in the mixture there are the 9 species I mentioned.

If you enable Volumetric reaction, and you look in the materials panel, you will see that there is only one reaction (that is the global reaction of hydrogen oxidation).

What I would like to know is: how can fluent calculate the concentrations of all the species in the mixture, if it apparently takes into account only one reaction, involving just H2, O2, and H2O?

I hope that now my question is more clear...

Regards,

Ale


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