# Henry's law solubility

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 April 28, 2016, 08:25 Henry's law solubility #1 Member   Michael Frank Join Date: Aug 2012 Posts: 45 Rep Power: 6 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

 May 24, 2016, 13:01 #2 New Member   Simone Colucci Join Date: Mar 2016 Location: Pisa (Italy) Posts: 13 Rep Power: 3 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

 May 24, 2016, 14:01 #3 Member   Michael Frank Join Date: Aug 2012 Posts: 45 Rep Power: 6 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

May 25, 2016, 05:50
#4
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Simone Colucci
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Quote:
 Originally Posted by mike.franky 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.

 May 25, 2016, 06:11 #5 Member   Michael Frank Join Date: Aug 2012 Posts: 45 Rep Power: 6 Yeah. I think that is the only thing that makes sense. Thanks. This has been very helpful

May 25, 2016, 06:16
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Simone Colucci
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 Originally Posted by mike.franky 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?

 May 25, 2016, 06:33 #7 Member   Michael Frank Join Date: Aug 2012 Posts: 45 Rep Power: 6 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?

May 25, 2016, 10:32
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Simone Colucci
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Quote:
 Originally Posted by mike.franky 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?

 May 25, 2016, 10:46 #9 Member   Michael Frank Join Date: Aug 2012 Posts: 45 Rep Power: 6 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.

May 25, 2016, 10:58
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Simone Colucci
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 Originally Posted by mike.franky 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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