I'm running some calcualtions with the diffusion and convection-diffusion modules in Comsol multiphyics. Recently I've encountered a strange phenomenon which I'd be very happy if someone had also encountered and handelled with:(adsbygoogle = window.adsbygoogle || []).push({});

First I take a simple 2 dimensional diffusion problem on a 1*1 cm square, taking two parallel sides to be insulating and on each one of the other sides i demand a certain different concentration, e.g. 0 and 1. Now Comsol does a perfect job for this very simple problem. Plus, if I'm trying to evaluate its success (by looking at the res_c_cd variable in the convection-diffusion module with zero convection) it gives very good results (residuals of about 1e-8).

However, if I take the same problem like before but now I'm demanding the concentrations only on a portion of the two parallel (let's say on half of each side I demand a certain different concentration and the other half I take as insulating) I get residuals of 7-8 orders of magnitude bigger than before, and more important I don't get flux conservation of the total system.

Please help me!

Thanks,

Uzik

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# Diffusion Module in Comsol Multiphysics

Can you offer guidance or do you also need help?

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