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error when coupling reactive flow and heat transfer
Posted 02.04.2014, 03:19 GMT-4 Fluid & Heat, Heat Transfer & Phase Change, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering Version 5.2 5 Replies
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Hello everyone,
I am a Comsol beginner and I am trying to model a turbulent reactive flow (homogeneous gasphase reaction).
I created a coupled model for the reactive flow and the heat transfer, very similar to the model "syngas combustion in a round-jet burner" in the library.
The model runs for the turbulent reactive flow (at least for some concentrations given in initial conditions and inflow) but when I try to couple it with the temperature, it first seems to converge pretty well but then gives this error:
Segregated group 4
Attempt to evaluate non-integral power of negative number.
- Function: ^
Failed to evaluate operator.
- Operator: nif
- Geometry: 1
- Boundary: 1 2 4 5 7
Failed to evaluate expression.
- Expression: nif((comp1.rspf.d_w_plus<(10/(comp1.rspf.Sc_wCO^0.33333333333333331))),nojac((comp1.rspf.d_w_plus*comp1.rspf.Sc_wCO)),(comp1.rspf.d_w_plus<sqrt(((comp1.rspf.kappav*1000)/comp1.rspf.ScT_wCO))),nojac(((15*(comp1.rspf.Sc_wCO^0.66666666666666663))-(500/(comp1.rspf.d_w_plus^2)))),nojac((((15*(comp1.rspf.Sc_wCO^0.66666666666666663))+((log(comp1.rspf.d_w_plus)*comp1.rspf.ScT_wCO)/comp1.rspf.kappav))-(((comp1.rspf.ScT_wCO*0.5)*(log(((comp1.rspf.kappav*1000)/comp1.rspf.ScT_wCO))+1))/comp1.rspf.kappav))))
Failed to evaluate variable.
- Variable: comp1.rspf.wplus_wCO
- Defined as: nif((comp1.rspf.d_w_plus<(10/(comp1.rspf.Sc_wCO^0.33333333333333331))),nojac((comp1.rspf.d_w_plus*comp1.rspf.Sc_wCO)),(comp1.rspf.d_w_plus<sqrt(((comp1.rspf.kappav*1000)/comp1.rspf.ScT_wCO))),nojac(((15*(comp1.rspf.Sc_wCO^0.66666666666666663))-(500/(comp1.rspf.d_w_plus^2)))),nojac((((15*(comp1.rspf.Sc_wCO^0.66666666666666663))+((log(comp1.rspf.d_w_plus)*comp1.rspf.ScT_wCO)/comp1.rspf.kappav))-(((comp1.rspf.ScT_wCO*0.5)*(log(((comp1.rspf.kappav*1000)/comp1.rspf.ScT_wCO))+1))/comp1.rspf.kappav))))
Failed to evaluate expression.
- Expression: d((down(comp1.rspf.rho)*comp1.rspf.beta0s^0.25*sqrt(max(comp1.k2,eps))*(comp1.rspf.wCOWall-comp1.wCO)*test(comp1.wCO)/comp1.rspf.wplus_wCO)*(dvol),{test@4})
- Feature: Stationary Solver 1 (sol7/s1)
Does anyone know what my mistake is?
BTW, it converges if I set all concentrations to zero.
Thanks for any hints!
Best regards,
Miriam
PS: The file is too big to upload, if it is any help I can try and cut it down.
I am a Comsol beginner and I am trying to model a turbulent reactive flow (homogeneous gasphase reaction).
I created a coupled model for the reactive flow and the heat transfer, very similar to the model "syngas combustion in a round-jet burner" in the library.
The model runs for the turbulent reactive flow (at least for some concentrations given in initial conditions and inflow) but when I try to couple it with the temperature, it first seems to converge pretty well but then gives this error:
Segregated group 4
Attempt to evaluate non-integral power of negative number.
- Function: ^
Failed to evaluate operator.
- Operator: nif
- Geometry: 1
- Boundary: 1 2 4 5 7
Failed to evaluate expression.
- Expression: nif((comp1.rspf.d_w_plus<(10/(comp1.rspf.Sc_wCO^0.33333333333333331))),nojac((comp1.rspf.d_w_plus*comp1.rspf.Sc_wCO)),(comp1.rspf.d_w_plus<sqrt(((comp1.rspf.kappav*1000)/comp1.rspf.ScT_wCO))),nojac(((15*(comp1.rspf.Sc_wCO^0.66666666666666663))-(500/(comp1.rspf.d_w_plus^2)))),nojac((((15*(comp1.rspf.Sc_wCO^0.66666666666666663))+((log(comp1.rspf.d_w_plus)*comp1.rspf.ScT_wCO)/comp1.rspf.kappav))-(((comp1.rspf.ScT_wCO*0.5)*(log(((comp1.rspf.kappav*1000)/comp1.rspf.ScT_wCO))+1))/comp1.rspf.kappav))))
Failed to evaluate variable.
- Variable: comp1.rspf.wplus_wCO
- Defined as: nif((comp1.rspf.d_w_plus<(10/(comp1.rspf.Sc_wCO^0.33333333333333331))),nojac((comp1.rspf.d_w_plus*comp1.rspf.Sc_wCO)),(comp1.rspf.d_w_plus<sqrt(((comp1.rspf.kappav*1000)/comp1.rspf.ScT_wCO))),nojac(((15*(comp1.rspf.Sc_wCO^0.66666666666666663))-(500/(comp1.rspf.d_w_plus^2)))),nojac((((15*(comp1.rspf.Sc_wCO^0.66666666666666663))+((log(comp1.rspf.d_w_plus)*comp1.rspf.ScT_wCO)/comp1.rspf.kappav))-(((comp1.rspf.ScT_wCO*0.5)*(log(((comp1.rspf.kappav*1000)/comp1.rspf.ScT_wCO))+1))/comp1.rspf.kappav))))
Failed to evaluate expression.
- Expression: d((down(comp1.rspf.rho)*comp1.rspf.beta0s^0.25*sqrt(max(comp1.k2,eps))*(comp1.rspf.wCOWall-comp1.wCO)*test(comp1.wCO)/comp1.rspf.wplus_wCO)*(dvol),{test@4})
- Feature: Stationary Solver 1 (sol7/s1)
Does anyone know what my mistake is?
BTW, it converges if I set all concentrations to zero.
Thanks for any hints!
Best regards,
Miriam
PS: The file is too big to upload, if it is any help I can try and cut it down.
5 Replies Last Post 16.04.2017, 11:28 GMT-4
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Posted:
1 decade ago
Hi Miriam,
Reactive flow model needs quite good initial values if you trying to couple it with temperature. This is the reason why "syngas combustion in a round-jet burner" model has been solved in steps: first step only reaction, second step only temperature and last step combination of both. Try this method.
If you want to send you model, you can try to clear solutions and mesh before sending model to forum.
Best regards
Tero Hietanen
Reactive flow model needs quite good initial values if you trying to couple it with temperature. This is the reason why "syngas combustion in a round-jet burner" model has been solved in steps: first step only reaction, second step only temperature and last step combination of both. Try this method.
If you want to send you model, you can try to clear solutions and mesh before sending model to forum.
Best regards
Tero Hietanen
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Posted:
1 decade ago
Hi Tero Hietanen,
thanks for the super fast reply!
unfortunately the file is still 5.2 MB after deleting all solutions etc.
If I try to do it in two steps, I do not get convergence for the temperature at all in the first step, it is rather a random error curve. So maybe the mistake has to be earlier, as the reactive flow is only working for some inflow concentrations. For others it gives me the same error as the coupled, though it seems to converge in the plot...
Any other tip how I could cut down the file further?
Thanks a lot!
Best regards,
Miriam
thanks for the super fast reply!
unfortunately the file is still 5.2 MB after deleting all solutions etc.
If I try to do it in two steps, I do not get convergence for the temperature at all in the first step, it is rather a random error curve. So maybe the mistake has to be earlier, as the reactive flow is only working for some inflow concentrations. For others it gives me the same error as the coupled, though it seems to converge in the plot...
Any other tip how I could cut down the file further?
Thanks a lot!
Best regards,
Miriam
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Posted:
1 decade ago
Hi,
I made a simplified 2D model which (hopefully) has the same problem. I attached it.
Thank you!
I made a simplified 2D model which (hopefully) has the same problem. I attached it.
Thank you!
Attachments:
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Posted:
1 decade ago
Hi,
I check you model and got it running. I only add boundary to "temperature1" .
Is this simplified version of full model? In this model you don't have any reaction or heat source. Is there any?
Best regards
Tero
I check you model and got it running. I only add boundary to "temperature1" .
Is this simplified version of full model? In this model you don't have any reaction or heat source. Is there any?
Best regards
Tero
Attachments:
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Posted:
8 years ago
Hi Miriam Vogt,
Could you solve the error you mentioned above as I happen to come across the same error when I tried to simulate a flow coupling reacting flow with heat transfer. Can you help me understand the real problem behind the error?
Thank you for your time.
regards
Raju
Could you solve the error you mentioned above as I happen to come across the same error when I tried to simulate a flow coupling reacting flow with heat transfer. Can you help me understand the real problem behind the error?
Thank you for your time.
regards
Raju