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Henry's law solubility

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Old   April 28, 2016, 08:25
Default Henry's law solubility
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Michael Frank
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Hi,

I am using the reactingMultiphaseEulerFoam to model migration of oxygen between a liquid and gas. The solution/dissolution of gases is modelled using Henry's law. Looking at the header file (Henry.h) i see that the model asks for the dimensionless Henry constant which is usually the ratio of the mass of the species in the liquid and gas. The source file however (Henry.C) multiplies the constant by the liquid density and divides by the gas density. This suggests that the input should actually be the volumetric ratio of the species. Is that correct? Should we give the values of k as the volume of the species in the liquid over the volume of the species in the gas?

Thanks in advance for your help

Cheers
Mike
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Old   May 24, 2016, 13:01
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Simone Colucci
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Hi Michael,
if you have a look into bubbleColumnEvaporatingDissolving the Henry constant for air dissolved in water is 1.492e-2 that corresponds to moles of gas dissolved per liter of solution/moles of gas, as you can see from here:

ftp://mana.soest.hawaii.edu/pub/rluk...0and%20Air.pdf

Simone
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Old   May 24, 2016, 14:01
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Hi Simone and thanks for your response.

I am slightly confused with the denominator. Could you please clarify? Is it the number of moles of the gas per unit volume outside the liquid?


Thanks again for your help
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Old   May 25, 2016, 05:50
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Quote:
Originally Posted by mike.franky View Post
Hi Simone and thanks for your response.

I am slightly confused with the denominator. Could you please clarify? Is it the number of moles of the gas per unit volume outside the liquid?


Thanks again for your help

I think so, is the number of moles of the component per unite volume in the gas phase, i.e. the gas-phase concentration of the component.
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Old   May 25, 2016, 06:11
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Yeah. I think that is the only thing that makes sense.

Thanks. This has been very helpful
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Old   May 25, 2016, 06:16
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Quote:
Originally Posted by mike.franky View Post
Yeah. I think that is the only thing that makes sense.

Thanks. This has been very helpful
Did you understand why there is liquid density divided by gas density?
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Old   May 25, 2016, 06:33
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Yes. Henry's constant is K=Cs/Cg (Cs is the concentration in solution and Cg in the gas). However, we don't directly have Cg. We have the percentage of that species in the total gas Yg. Also, the function in Henry.C actually returns the percentage of the species in the solution, Ys. So
Cs = Ys*Rs (mass of the specific species per unit volume of solution)
Cg = Yg*Rg (mass of the specific species per unit volume of gas)
where Rg and Rs are the densities of the gas and solution.

Inserting these into the first equation and re-arranging a bit we get:
Ys = K*Yg*Rg/Rs


Does that make any sense?
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Old   May 25, 2016, 10:32
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Quote:
Originally Posted by mike.franky View Post
Yes. Henry's constant is K=Cs/Cg (Cs is the concentration in solution and Cg in the gas). However, we don't directly have Cg. We have the percentage of that species in the total gas Yg. Also, the function in Henry.C actually returns the percentage of the species in the solution, Ys. So
Cs = Ys*Rs (mass of the specific species per unit volume of solution)
Cg = Yg*Rg (mass of the specific species per unit volume of gas)
where Rg and Rs are the densities of the gas and solution.

Inserting these into the first equation and re-arranging a bit we get:
Ys = K*Yg*Rg/Rs


Does that make any sense?
The formula that you reported is the implemented one in Henry.C, but if C indicates the number of moles of the component per unite volume, the right formula should be:

Ys = K*Yg*Rg/Rs*Ms/Mg

where M is the molecular weight.
Is something missing in the code?
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Old   May 25, 2016, 10:46
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Yes. But you are forgetting that Ms and Mg refer to the same species, i.e. whether oxygen is dissolved in a liquid or free in a gas, it always has the same molecular mass.
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Old   May 25, 2016, 10:58
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Yes. But you are forgetting that Ms and Mg refer to the same species, i.e. whether oxygen is dissolved in a liquid or free in a gas, it always has the same molecular mass.
You are right!
Thanks!
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