Discussion Forum

At internal boundaries you do not need to specify any BC, unless you need something particular. Comsol takes care of the continuity of concentration and flux. You just define the transport coefficient in the adjacent phases. What do you have in mind?

BR
Lasse

Thank you sir,
I have 2 layers one above the other (2 concentric layers on a sphere) having different materials, both layers have different diffusion coefficients (D1, D2). 1st layers is made up of 'c1' and 2nd layer is made up of 'c2'.
The material of my interest is 'c1'.
'c1' has to diffuse through the 2 layers. In the second layer it has to diffuse through 'c2'.

How can I model this system?
If I am using 2 Transport of diluted species physics separately for these 2 layers, what should be my boundary at the interface of these 2 layers?

I am modeling in 2D axisymmetric

You do not need two physics nodes, just define different diffusion coefficients in the two layers, as well as initial concentrations. If possible, please submit your model.

BR
Lasse

Hi Lasse

But if you only use one physic node you will only have one concentration (one variable name) for the two domains, isn't that right?

What can I do if I want to have two different concentrations (two variable names), one in each domain and I want to maintain the flux continuity condition between the two domains?

Thank you

Best wishes

Javier

Hi

You have to define a permeability coefficient for the interface. Let's say that in domain you have C1 and in domain 2 C2, and the permeability coefficient is Kp (cm/s). If the flux is going from domain 1 to domain 2, write a Flux BC in domain 1:

Flux = -Kp*(C1 - C2)

and in domain 2

Flux = +Kp*(C1 - C2)

If Kp is very large, it means that the flux is diffusion limited.

Wish this helps; this is how I have done it.

BR
Lasse

Thank you very much for your answer, Lasse. I am going to try it.

BR

Javier