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Flux boundary condition

Posted Apr 24, 2019, 1:15 p.m. EDT Chemical, General Version 5.4 2 Replies

Mayuri Ukidwe
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I recently noticed the flux boundary condition in the new version is different from the old versions. For the flux boundary n.j=j_0 is j in the domain always considered as the diffusive j=-D(grad c) in the newer version? If I enable convection in the domain, does this the flux automatically switch to j=-D(grad c)+uc or I will have to manually adjust for the convective flux (uc) in terms of expression of j_0?

2 Replies Last Post Apr 30, 2019, 11:16 p.m. EDT
Lasse Murtomäki
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Posted: 6 years ago Apr 25, 2019, 6:02 a.m. EDT

Note that the normal component of u is zero, unless the boundary is permeable. How do you think that the flux would only be diffusion? What is your model like?

Note that the normal component of u is zero, unless the boundary is permeable. How do you think that the flux would only be diffusion? What is your model like?
Mayuri Ukidwe
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Posted: 6 years ago Apr 30, 2019, 11:16 p.m. EDT

Hi Lasse,

I am using transport of diluted species with convection and diffusion in the conservative form. There is a constant inwards flux of the species at the boundary. My question is about the default expression for the flux j inside the domain. In my understanding if I have convective and diffusive transport in the domain then, flux at the boundary j_0 = -D(gradC)+uC The expression in comsol states n.j=j_0 In the earlier versions the j in the 'Transport' was defined as -D(gradC)+uC In the new version is only diffusive flux (Screenshot attached)?

Mayuri

Hi Lasse, I am using transport of diluted species with convection and diffusion in the conservative form. There is a constant inwards flux of the species at the boundary. My question is about the default expression for the flux **j** inside the domain. In my understanding if I have convective and diffusive transport in the domain then, flux at the boundary j_0 = -D(gradC)+**u**C The expression in comsol states **n.j**=j_0 In the earlier versions the **j** in the 'Transport' was defined as -D(gradC)+**u**C In the new version is only diffusive flux (Screenshot attached)? Mayuri

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