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Chemical reaction between gas and solid through a porous media

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Old   May 10, 2022, 13:52
Default Chemical reaction between gas and solid through a porous media
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Hi everyone,

I want to model a gas flow through a porous media with a chemical reaction. The chemical reaction is : 2HF + CaCO3 = CaF2 + CO2 +H2O where the gas is the HF and the CaCO3 (solid state) is the porous media.

I've looked through the tutorials and tried to adapt the chapter 15. I've computed the different source terms for my reaction. The subdomain in my porous media is defined.

The model gives no errors but the results are not good. I can only visualize the HF masse fraction but it does not seem to be affected by the reaction, other mass fraction are equal to 0. In short, the reacton does not occur.

Any help would be greatly appreciated!
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Old   May 10, 2022, 16:48
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Would you mind sharing what those source terms look like?

Did you do it via CEL, or using built-in reaction modeling?
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Old   May 10, 2022, 16:56
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I did it via the CEL
I've copied the CEL files of the tutorial (Chapter 15) and changed it with the values of my reaction. I added expression for each product of the reaction.

The CCL file is joined with the reply
Attached Files
File Type: txt ReactorExpressions.txt (1.9 KB, 12 views)
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Old   May 10, 2022, 17:30
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I am a bit confused by your expressions.

CaCO3 is the solid matrix; therefore, the concept of mass fraction, CaCO3.mf does not exists. Mass Fractions are variables for the multicomponent phase.

I am surprised you did not get an error for such usage.

Also, you seem to have taken the Eddy Dissipation route for the combustion, not the finite rate chemistry mechanism. Not certain Eddy Dissipation makes sense for such a reaction.
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Old   May 10, 2022, 17:48
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Hmm, I was afraid of that but I tried it anyway, did not work.

Quote:
Originally Posted by Opaque View Post
I am surprised you did not get an error for such usage.
I guess a second error balanced for the first..

In the tutorial, the Eddy break up formulation is used, it doesn't seem to be a combustion on this case, I thought I could also use it.
I will try the finite rate chemistry model and hope it will work.

Thanks for the advice
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Old   May 17, 2022, 17:13
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Hi,

I tried to use the finite rate chemistry model for the same chemical reaction: 2HF + CaCO3 = CaF2 + CO2 +H2O

I've defined the chemical reaction as follows

LIBRARY:
&replace REACTION: Reaction 1
Object Origin = User
Option = Single Step
COMBUSTION MODEL:
Chemical Timescale = 1.37E-4 [s]
Extinction Temperature = 900 [K]
Option = Finite Rate Chemistry
END
FORWARD REACTION RATE:
Option = Expression
Reaction Rate = -7.72e-11 [mol m^-3 s^-1]
END
PRODUCTS:
Materials List = CO2,CaF2,H2O
Option = Child Materials
CHILD MATERIAL: CO2
Option = Stoichiometric
Stoichiometric Coefficient = 1.0
END
CHILD MATERIAL: CaF2
Option = Stoichiometric
Stoichiometric Coefficient = 1.0
END
CHILD MATERIAL: H2O
Option = Stoichiometric
Stoichiometric Coefficient = 1.0
END
END
REACTANTS:
Materials List = CaCO3,HF
Option = Child Materials
CHILD MATERIAL: CaCO3
Option = Stoichiometric
Stoichiometric Coefficient = 1.0
END
CHILD MATERIAL: HF
Option = Stoichiometric
Stoichiometric Coefficient = 2
END
END
END
END

The material (mixture reaction) is defined (reactant, product, and air).
Fluid model: air on constraint, others on transport equation.
I'm still not able to see the product of reaction (mf = 0)...

Also, the CaCO3 in the porous domain is supposed to be transformed into CaF2. How can I define the change of material in the porous domain during the reaction process?

Thanks
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