Problems using radiative heat transfer in Comsol

[curros38]

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.

 

[snorky]

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.

 

[oswaler]

Hi there,

Thank you for sharing your experience with Comsol and your question about using radiative heat transfer. It sounds like you have already made some progress in solving your problem by using the Electro-Thermal Interaction Application Mode and considering conduction heat transfer. However, when attempting to implement radiation, you encountered an error message involving complex numbers and are unsure of how to proceed.

Based on the information provided, it is difficult to determine the exact cause of the error. However, it is possible that there may be an issue with the way you have defined the boundaries or expressions in your model. I would recommend double-checking all of your inputs and boundary conditions to ensure they are correctly defined.

Additionally, it is possible that there may be a bug in the program that is causing the variable T to become a complex number. In this case, I would suggest reaching out to Comsol's technical support team for assistance. They may be able to provide more specific guidance and help troubleshoot the issue.

In general, when working with complex systems and simulations, it is not uncommon to encounter unexpected errors or issues. It is important to carefully review your inputs, seek assistance from technical support, and potentially consult with other experts in the field to find a solution. I wish you the best of luck in solving your problem and successfully implementing radiative heat transfer in your model.