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surface exchange b.c.

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Old   January 8, 2008, 03:45
Default surface exchange b.c.
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I have done a number of models with the built in physics modes of Comsol 3.3 Now I need a special bc that's not builtin and need some advice.

For a 1-d model, the bc (boundary condition) is for diffusion flux determined by a surface exchange coefficient:

j=k (c1-c2*B)

where j is the flux (=-Ddc/dx on left and right of the boundary) k is const c1 is concentration on left of boundary c2 is concentration on right of boundary B is const

I thought of exploiting the builtin boundary equations where one has


and setting cb appropriately, but this isnt right as my bc is still conservative (what flows out of one side flows into the next) so n(N1-N2)=0.

The boundary concentrations are apparently available thru the 'up' and 'down' functions to access the values of c just before and after a boundary , how do i define a bc to use these? Do I need to use 'weak form' if I only want to set the tangential derivative j=k (c1-c2*B)=-D dc/dx

Also is there a spherical symmetry model setup?

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