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richard ben April 9, 2013 04:26

species transport model simulating chemical reaction
 
2 Attachment(s)
Hi everyone,

I am using the species transport model to simulate a chemical reaction.

First, I use the non-reactive simulation and it is converged,

then I enable the species transport model to simulate the reactive flow, however

it iterates only once and is converged. I check the quantity of the product, and its order of magnitude is -10 or less. I have no idea how to set up any other parameters.

I have no idea whether I make myself understood. And I will appreciate a lot for your help.

asal April 9, 2013 08:02

Hi!

If I understand your question correctly, you have to check the Solution => Monitor, Edit the residuals and reduce the convergence criteria or un-check it. your residuals are fall below to the set criteria!

richard ben April 9, 2013 09:12

hi asal,

thank you very much for your reply. i think the preoblem is : before any products produced, the iteration is converged. the reactive simulation only iterated once. the iteration shown in the above picture is due to the non-reactive simulation. so do i make myself understood? can you give my more advice?

thank you again

asal April 9, 2013 09:56

Hi!

Do you check the monitor residuals which I mentioned before?!
When you want to simulate the reactive flow, some residuals will added to the residuals criteria list to control the convergence. for instance you had one more residuals for NOx. Since your residuals fall below to the predefined number in the residuals criteria, after one iteration, you run stop due to achieving converge solution.

cinwendy April 9, 2013 10:09

Hi!

What Richard encountered was what I encountered before. At the end I didn't look at residual when I am dealing with reactive species AFTER I have the flow field calculated. I set up other monitor and monitor it seperately, and then decide when to stop calculation.

Does this helps?

richard ben April 9, 2013 10:27

Hey, asal,

I appreciate your reply a lot. I did try to reduce the residuals, and it iterated more steps. However I didn't get the correct result. Since after it was converged, I check the quantity of the producta again and their order of magnitude were the same.

I think the problem might some of the inputs. Since I changed the rate exponent in the reaction dialog box, the result is acceptable. I don't how to input some of the parameters: the rate exponent and temperature exponent.

It might be helpful that I write the reactions:

NiFe2O4 ----> NiO + 2 FeO +1/2 O2

NiO + 2 FeO + H2O ----> NiFe2O4 + H2

They are wall surface reactions

richard ben April 9, 2013 10:52

Quote:

Originally Posted by cinwendy (Post 419438)
Hi!

What Richard encountered was what I encountered before. At the end I didn't look at residual when I am dealing with reactive species AFTER I have the flow field calculated. I set up other monitor and monitor it seperately, and then decide when to stop calculation.

Does this helps?

Hey, cinwendy,

Thank you for your help. I didn't get you. What other monitors did you set?

richard ben April 9, 2013 11:42

Hey, asal,

I am sure the problem is the rate exponent. Since I tried different rate exponents and got different results.

The rate exponent of NiFe2O4 is 1 and if I change it, no result.

I am not sure what are the rate exponents of NiO, FeO and H2O, but not stoichimetric coeeficient. I don't know how to calculate them. Do you?

cinwendy April 10, 2013 01:06

Quote:

Originally Posted by richard ben (Post 419446)
Hey, cinwendy,

Thank you for your help. I didn't get you. What other monitors did you set?

Opps, sorry for not explaining clearly enough.

I set up volume monitor for the reactive species. I still let the residual to be monitored but uncheck the convergence ctiretia. So I manually stop the calculation when the volume monitor of the species has reached steady value.

Currently I still do this manually, I couldn't find a way to make it a "convergence criteria" to stop iteration like the residue.

richard ben April 10, 2013 08:57

Quote:

Originally Posted by cinwendy (Post 419538)
Opps, sorry for not explaining clearly enough.

I set up volume monitor for the reactive species. I still let the residual to be monitored but uncheck the convergence ctiretia. So I manually stop the calculation when the volume monitor of the species has reached steady value.

Currently I still do this manually, I couldn't find a way to make it a "convergence criteria" to stop iteration like the residue.

I solved my problem by setting the correct rate exponent of the reactants.
Maybe you can try.


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