What should be done when the reaction rate is too high?

MFiX How to
#1

I am simulating a case where I used a commonly used reaction kinetics and parameters, but it did not converge. When the reaction rate was multiplied by 0.0001, the reaction converged and could be run normally. The conclusion that can be drawn is that the reaction rate is causing the non-convergence, but is my method correct? Or will the result have an impact on the previous one?

#2

Hi @qianbinhui
You are correct that excessively high reaction rates can cause non-convergence. I suggest that you check that you are using the correct units.

I’m not sure what you mean “the result have an impact on the previous one”. And as usual, please attach your files if you want us to have a look.

– Charles

#4

1.zip (50.7 MB)

2.zip (26.3 MB)

if the reaction rate is too high and then multiplied by 0.0001, will the result have an impact? Secondly, my units are fine, here is my case, thank you for your reply.

#6

hi,It can be seen that it is a problem with the soaring temperature, or something else, as this is a validation model, and if it needs to be multiplied by a coefficient to converge, it should be a problem with my setting.

#7

Hello, after multiplying by 0.0001, will the result change? For example, the amount of biomass particle reaction is relatively small. What is the correct solution
@cgw

#8

@jeff.dietiker ，@cgw
Can someone help me

#9

If you multiply the reactions rates by 0.0001, you should expect the results to change, unless the reaction is already negligible. We cannot tell you what is the correct value. My suggestions are:

  1. Start with a single particle simulation and verify the reaction rates you get from your coded usr_rates.f and usr_rates_des.f are what you expect from hand calculation.
  2. Double check the heat of formation for each species.
  3. Use the stiff chemistry solver if the reaction rates are very large.
#10

Hello, * 0.0001 does have an impact on the results. I have kept the stiff chemistry option open, and my heat of formation for each species is 0.0. I am very interested in the first method you mentioned, how it was calculated, because the values of A and E in this reaction rate are obtained from literature.
thanks for your reply

#11

Hello everyone, without multiplying by a coefficient, I can now converge. I mainly changed the particle model, and pyrolysis is more suitable for models with variable particle size and constant de

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nsity. Secondly, I added reaction heat, so it converges.

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