[Khan_CFD]

Hi.

I am simulating simultaneous heat transfer and chemical reaction problem.

There are two fluids separated by a solid wall. On each side of the wall-fluid interface, a reaction takes place. One side an endothermic and other side an exothermic.

The heat transfer through the coupled wall seems OK.

There is N2 gas in one of the streams and no N2 in other one. It does not participate in reaction. But, after simulation is completed, mass fraction of N2 is shown to increase along the length of the reactor. Also, N2 is shown in other fluid, in which I have not given any N2 in the inlet...??

Is it something with the ordering of species in selected species section..?

Ansys help section says the last species is not calculated in transport equations and also that highest mass fraction species (carrier gas) should be the last one in the list. But the mass fraction of that species could decrease in the course of reaction and it might not be the highest mass fraction say midway in the reactor (rectangular channel). In that case which species should be selected as the last one.

Did I identify the problem right? Is there any other issue I need to address?

Any help is deeply appreciated..!

Thanks.

[Jegan]

Hello,
I can say only this....Last species is the bulk species.. you should arrange according to that in species list. In the species tab bulk species(last_species) will not appear,which means fluent calculate the rest of mass fraction to that species.for example if u give 0.21 for oxygen then the last species will be considered automatically as 0.79.
sorry for my English..hope this will help you

[Khan_CFD]

Originally Posted by Jegan

Hello,
I can say only this....Last species is the bulk species.. you should arrange according to that in species list. In the species tab bulk species(last_species) will not appear,which means fluent calculate the rest of mass fraction to that species.for example if u give 0.21 for oxygen then the last species will be considered automatically as 0.79.
sorry for my English..hope this will help you

Thanks Jegan for your help. I figured that the component that will have highest mass fraction in the inlet should be the last species, then numerical error will be minimized in species balance as fluent does not calculate transport equation for that species but takes it as 1- (sum of mass fractions of remaining all species).

In case the mass fraction of one component is highest at inlet but mass fraction of other component becomes highest during the course of reaction, then I guess something like 'which component will have highest mass fraction in 'overall' should be taken as last species. What this 'overall' means, I am not sure.