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Mass balance is break

Posted Mar 10, 2011, 4:50 a.m. EST Computational Fluid Dynamics (CFD), Chemical Reaction Engineering Version 4.1 11 Replies

Kim Daehun
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Hello

My problem is mass balance of reactant and product materials.

total number of component is five. and reaction is A+2B=>C+4D

turbulent module and transport of concentrated species module and Heat transfer module is coupled.

the simulation is converged at tolerance 1e-5 but component mass balance is break.

how can i solve the problem ?

i don't know.............
11 Replies Last Post Mar 16, 2011, 9:17 a.m. EDT
Mayur
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Posted: 1 decade ago Mar 10, 2011, 9:18 a.m. EST
post your comsol file..
post your comsol file..
Kim Daehun
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Posted: 1 decade ago Mar 11, 2011, 7:13 a.m. EST
this is my file !!!
this is my file !!!

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Mayur
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Posted: 1 decade ago Mar 11, 2011, 7:52 a.m. EST
no attachment
no attachment
Kim Daehun
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Posted: 1 decade ago Mar 11, 2011, 7:56 a.m. EST
Oh !!!!

sorry !!

i do mistake !!

i attached the model ~~
Oh !!!! sorry !! i do mistake !! i attached the model ~~
Kim Daehun
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Posted: 1 decade ago Mar 11, 2011, 8:13 a.m. EST
new file
new file

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Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 11, 2011, 4:14 p.m. EST
Hi

could it be because you are working at an absolute pressure of 2[atm] ? as you have a gauge pressure of 1[atm] in the turbulent flow, to which you add an absolute pressure again of 1[atm]. Probably you should work at a gauge pressure of "0" in the turbulent flow (both inlet and outlet). But I'm not a CFD/chemistry expert, so pls check carefully ;)

--
Good luck
Ivar
Hi could it be because you are working at an absolute pressure of 2[atm] ? as you have a gauge pressure of 1[atm] in the turbulent flow, to which you add an absolute pressure again of 1[atm]. Probably you should work at a gauge pressure of "0" in the turbulent flow (both inlet and outlet). But I'm not a CFD/chemistry expert, so pls check carefully ;) -- Good luck Ivar
Mayur
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Posted: 1 decade ago Mar 11, 2011, 4:48 p.m. EST
Hi,
here is the solution, first you should use weakly compressible flow for your continuity equation to be conserved instead of incompressible. You will realise this after comparing both the incompressible and weakly compressible equations. Second is you need to use the conservative form of convection-diffuion equation, but in your case you are using concentrated form of convection-diffusion physics that I still have to look at in detail. I think first just try using compressible form, your rho*u quantity must be conserved.
Cheers
Mayur
Hi, here is the solution, first you should use weakly compressible flow for your continuity equation to be conserved instead of incompressible. You will realise this after comparing both the incompressible and weakly compressible equations. Second is you need to use the conservative form of convection-diffuion equation, but in your case you are using concentrated form of convection-diffusion physics that I still have to look at in detail. I think first just try using compressible form, your rho*u quantity must be conserved. Cheers Mayur
Kim Daehun
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Posted: 1 decade ago Mar 15, 2011, 1:36 a.m. EDT
Hello !!

i simulated the diluted species module. and use conserved form.

but i still have the similar problem !!

total mass flux is conserved. but component mole flux is break

A+2B --> C+4D

reactant B reacted more than 2mole..........

how can i solve the problem . ?

file size is 19MB so i don't attached simulated results.



Hello !! i simulated the diluted species module. and use conserved form. but i still have the similar problem !! total mass flux is conserved. but component mole flux is break A+2B --> C+4D reactant B reacted more than 2mole.......... how can i solve the problem . ? file size is 19MB so i don't attached simulated results.

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Mayur
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Posted: 1 decade ago Mar 15, 2011, 9:22 a.m. EDT
let me know the total normal flux of each component at inlet and outlet boundaries by integrating them in following form. The unit for the total normal flux for 2d model should be in mol/m/s. Again remember you have to integrate it on each boundary.


Components Inlet total molar Flux Outlet total molar flux

A
B
C
D
let me know the total normal flux of each component at inlet and outlet boundaries by integrating them in following form. The unit for the total normal flux for 2d model should be in mol/m/s. Again remember you have to integrate it on each boundary. Components Inlet total molar Flux Outlet total molar flux A B C D
Kim Daehun
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Posted: 1 decade ago Mar 16, 2011, 2:07 a.m. EDT
Hi !!

my model is axial symmetry !!

so, the unit of mass rate is mol/s !!

and i consider a density change in my system. so i select concentrated species module !

but when i choose compressible flow(Ma<0.3), i have a error

( incompressible flow is not !! it has not error )

error massage is attached. !!
Hi !! my model is axial symmetry !! so, the unit of mass rate is mol/s !! and i consider a density change in my system. so i select concentrated species module ! but when i choose compressible flow(Ma

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Mayur
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Posted: 1 decade ago Mar 16, 2011, 9:17 a.m. EDT
but for incompressible flow you won't be able to conserve rho*u quantity which is not acceptable under any situation.. if possible contact support, they will help you with this error message..
good luck
Mayur
but for incompressible flow you won't be able to conserve rho*u quantity which is not acceptable under any situation.. if possible contact support, they will help you with this error message.. good luck Mayur

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