Why do you need to specify a partition condition if you already know a species' permeability in a domain?

Rogelio Garcia Fernandez

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Hello community!

If a chemical species is moving (by concentration difference) from one liquid domain to a solid domain and then to another liquid domain, do you need to specify partition conditions at the two liquid-solid interfaces?

Shouldn't a simulation give realistic results if we just specified the chemical species' diffusion coefficient in the liquid phases and its permeability coefficient in the solid phase?

Is one overspecifying the diffusion model by including partition conditions?


3 Replies Last Post 26 Oct 2020, 08:02 GMT-4

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Posted: 1 month ago 25 Oct 2020, 01:42 GMT-4

If you know the overall permeation coefficient (Kp) from, say, experiments, that would include partitioning. But if you just know the mobility (diffusion coefficient, D) of the transferring species in the solid, you need to take into account the partition coefficient, P.

Kp = PD/h (h = thickness of the solid phase)

Note that you need to consider partitioning on the both sides of the solid phase.

If you know the overall permeation coefficient (Kp) from, say, experiments, that would include partitioning. But if you just know the mobility (diffusion coefficient, D) of the transferring species in the solid, you need to take into account the partition coefficient, P. Kp = PD/h (h = thickness of the solid phase) Note that you need to consider partitioning on the both sides of the solid phase.

Rogelio Garcia Fernandez

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Posted: 1 month ago 25 Oct 2020, 16:54 GMT-4

If you know the overall permeation coefficient (Kp) from, say, experiments, that would include partitioning. But if you just know the mobility (diffusion coefficient, D) of the transferring species in the solid, you need to take into account the partition coefficient, P.

Kp = PD/h (h = thickness of the solid phase)

Note that you need to consider partitioning on the both sides of the solid phase.

Thank you so much for your contribution. I really apprecite your time. One more question:

Is the partition coefficient the same at both sides of the solid phase? If so, what about if only one interface is expose to a liquid face with force convection?

>If you know the overall permeation coefficient (Kp) from, say, experiments, that would include partitioning. But if you just know the mobility (diffusion coefficient, D) of the transferring species in the solid, you need to take into account the partition coefficient, P. > >Kp = PD/h (h = thickness of the solid phase) > >Note that you need to consider partitioning on the both sides of the solid phase. Thank you so much for your contribution. I really apprecite your time. One more question: ***Is the partition coefficient the same at both sides of the solid phase? If so, what about if only one interface is expose to a liquid face with force convection?***

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Posted: 1 month ago 26 Oct 2020, 08:02 GMT-4

Partition coefficient is purely a chemical quantity, the exponent of the difference between the stadrard chemical potentials in the two phases over RT:

P = exp[(µ°(1) ─ µ°(2))/RT]

Cheers Lasse

Partition coefficient is purely a chemical quantity, the exponent of the difference between the stadrard chemical potentials in the two phases over RT: P = exp[(µ°(1) ─ µ°(2))/RT] Cheers Lasse

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