CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   FLUENT (http://www.cfd-online.com/Forums/fluent/)
-   -   ISAT reaction rate error for modeling the flare (http://www.cfd-online.com/Forums/fluent/93775-isat-reaction-rate-error-modeling-flare.html)

Rouzbeh1360 October 26, 2011 08:45

ISAT reaction rate error for modeling the flare
 
Hi,

I use Fluent to model an industrial flare and I have considered SO2 reaction mechanism for this purpose. However, as the time that I run the model, after some iterations, it gives me the following error:
ISAT reaction rate: Temperature = -2202509.1 K
The velocity of the gas exiting from the stack is 0.54 m/s
Stack diameter is 20 cm
And I did not have the same problem with other reaction mechanism (CH4 mechanism) that I previously worked with (all of the conditions except the mechanism are the same).
I wonder if anyone knows the reason?

Thanks in advance,
Rouzbeh

Basy November 15, 2011 04:33

Ruzbeh
I'm having same problem with mechanisms. please let me know if you have found the answer so far. I'll post here if i can figure out the solution.

regards
behzad

Basy November 15, 2011 05:21

Dear rouzbeh
I was trying to calculate a flamelet (non-premixed combustion, steady laminar flamelet) and I got that error. I referred to FLUENT manual (18.3.2) and read a little about this ISAT...quite tough math...but I noticed it mentioned that error tolerance maybe better reduced for some cases...in "Species Model">"Contorl" I reduced my relative error tolerance to 1e-20 and absolute error to 1e-25. the flamelet is generated with no problem (but it was too quick, maybe some thing is wrong) I am not sure at the moment I have to proceed and do the simulation and see if its really ok or not...I hope that has helped you.

Basy November 16, 2011 15:50

yeah...everything was ok...it worked properly

Rouzbeh1360 November 28, 2011 17:52

Thanks. I will do the same thing see whats happen.

xmaspako February 9, 2012 06:23

thanx a lot, Basy.
You've solved my problem.

I had a similar problem in EDC (also with direct integration active). Exactly problem was: ISAT reaction rate: Temperature = 0.1K.

Thanx again

:D

Basy February 9, 2012 08:05

You are most welcome dear xmaspako, but please be careful...

I have to update my posts, that the result I got was NOT 100% OK and was greatly inaccurate. So there is a chance that for your problem things don't work good either. You have better have it in mind and check your result's accuracy carefully.

here is some details of my work and I hope that helps. I was solving turbulent combustion with steady laminar flamelet and I was trying to develope a flamelet with a detailed reaction mechanism developed in ploy-technique of Milan for methane, and I encountered this error. I temperarily solved my problem as I explained earlier but later i noticed my results are not accurate at all. Finally I learned that the problem was that this reaction mechanism was designed with a sort of reaction rates that are not compatible with Fluent6.3 and that leads to ISAT error (And I have to say I still don't know whether this problem can be fixed with some manipulation of ISAT integration in Fluent6.3 or not) . I developed the flamelet with no problem by Fluent 12.


good luck :)

xmaspako February 9, 2012 08:58

Hi Basy.
Thanx for alert. I'm using Fluent V13, instead. Reactions are between Air and Hydrogen with a external chemkin model. I hope results are good... but iterations are still running... when I reach steady state, I'll check them.

I'll keep you informed

rezareal April 16, 2013 08:04

Error: ISAT reaction rate: Temperature = 0.1K Error Object: ()
 
Hi
I'm working with an EDC model with 3 nozzles for injection of urea but Unfortunately after some iterations, it gives me the following error:

Error: ISAT reaction rate: Temperature = 0.1K
Error Object: ()
I also changed relative error tolerance and absolute error
but I still have the same problem.

please help me
thanks

cryogenicT August 3, 2013 16:57

Quote:

Originally Posted by Basy (Post 332148)
Dear rouzbeh
I was trying to calculate a flamelet (non-premixed combustion, steady laminar flamelet) and I got that error. I referred to FLUENT manual (18.3.2) and read a little about this ISAT...quite tough math...but I noticed it mentioned that error tolerance maybe better reduced for some cases...in "Species Model">"Contorl" I reduced my relative error tolerance to 1e-20 and absolute error to 1e-25. the flamelet is generated with no problem (but it was too quick, maybe some thing is wrong) I am not sure at the moment I have to proceed and do the simulation and see if its really ok or not...I hope that has helped you.

It's an old thread but I have a quick remark. These tolerances (RE = 1.0e-20 and AE = 1.0e-25) are too small, smaller than your machine precision. You need set more reasonable values for faster convergence. The default values, RE = 1.0e-10 and AE = 1.0e-14, are sufficiently small and work just fine. You will not notice any differences in the results.

sunyilsh May 15, 2014 08:45

Quote:

Originally Posted by rezareal (Post 420901)
Hi
I'm working with an EDC model with 3 nozzles for injection of urea but Unfortunately after some iterations, it gives me the following error:

Error: ISAT reaction rate: Temperature = 0.1K
Error Object: ()
I also changed relative error tolerance and absolute error
but I still have the same problem.

please help me
thanks

Hello!
I am working at similar subject with you and meet the same question. Would you please help me solve the problem? (ISAT reaction 0.1K)
Thank you!


All times are GMT -4. The time now is 20:18.