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Problems using radiative heat transfer in Comsol

  1. Oct 24, 2009 #1
    Hi everyone. I am starting using Comsol modeling the temperature field of a buried cable installed into a PVC duct (2D problem). I have already solved the problem considering heat transfer by conduction. To do this, I have used the Electro-Thermal Interaction Application Mode (Perpendicular induction heating: Steady-state) included in the AC/DC Module. However, when I try to implement radiation I have this message:

    Error: 6253
    Complex number found in irradiation expression.
    - Expression: J
    - Geometry: 1
    - Boundaries: 5,6,7,8,13,14,17,18
    Failed to evaluate expression.
    - Expression: d(((dVolbnd_htgh*epsilon_htgh*(Gm_htgh+Famb_htgh*sigma_htgh*Tamb_htgh^4-sigma_htgh*T^4)*test(T))-(0))*(dvol),{test@0})

    I think the problem is that in this application mode the variable T has become a complex number (I don´t know why, but it´s true. When I click on the T surface plot I get this: Value: 341.171896-6.440595e-6i [K], Expression: T, Position: (-0.013275,-0.006)).

    Could this behaviour be a program bug? or Should I have to change anything in my model to make variable T a real number again?
    I hope someone can help me.

    Thank you for your suggestions.
  2. jcsd
  3. Nov 2, 2009 #2
    Dear Curros,

    Please reevaluate your material parameters.

    Example: if your temperature is relative (as on overtemperature with respect to ambient) then it is possible to be 0.

    COMSOL evaluates the properties with the absolute temperature (ambient+relative for the given example), so if your model has 0 in reality should be Tambient+T.
    I hope you get the idea.
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