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Hi,

Conjugate Heat Transfer and Non-isothermal Flow should be using same physics. In Conjugate Heat Transfer default volume is solid and in Non-isothermal Flow volume is fluid. You can add missing fluid/solid volume by right mouse click over current physics.

Did you make both simulation identical?

Best regards

Tero

First of all thank you very much. :)

I made identical model(by adding solid to Non-isothermal Flow and the fluid to the Conjugate Heat Transfer) and boundary conditions in both of them but the result is very different and it is not clear for me which one is correct.

In addition to this problem, in conjugate heat transfer module when I draw a simple 2D model it will be solved almost correct, but when I draw the same model in 3D with the same boundary conditions the answer could not be converged. What does this error exactly mean? Should I work more on boundary conditions or the problem is fundamental?

Hi,

I have to check this by myself and see if something is wrong...

I will contact you later.

Br Tero

Hi,

I tested both versions and I couldn't find any difference between Non-isothermal Flow and Conjugate Heat Transfer. Also I check results with older version, 4.2a, and between version there was small difference. Models were made in 3D and I had no convergence problems.


Br

Tero

Hi again,

Thank you so much for your kind help :)
I am wondering if you could find some time and check the attached files to see the difference in result of two modules while the geometry and boundary conditions are the same.
In one of them maximum temperature is 656 K while in the other one it is 1055 K!

If you can not, would you please tell me for my case which one is the best?
There is a closed cylinder (made of steel). Inside it there are some components like heat sources and the fluid is Nitrogen (1 atm). We need to investigate heat transfer and and find hot spots and max temperature.

Best regards,
Razieh

Hi,

Here are fixed versions. Now both are giving similar results. I changed in Conjugate Heat Transfer => Fluid1 => Model Inputs => "Make All Model Inputs Editable" section off (check picture) and after this both are giving similar results. There are also other changes but I this was making biggest difference.

I prefer to use Non-Isotermal Flow.

Best regards

Tero

Hi again,

Thank you so much for your useful help about my previous questions. Now I have another technical question regarding the volume force in non-isothermal flow in Heat Transfer module. According to COMSOL examples such as heat transfer of circuit boards it is reasonable to use -g_const*rho instead of volume force. But the circuit board example has only one circulation path in one direction for cooling in the opposite direction of gravity.
For my model we have one vertical big closed canister filled with gas and inside it we have an vertical open smaller cylinder which has some heat sources inside, so there are more than one path for circulation and cooling.(the attached file of previous posts contains a simplified model)
What can be the volume force here? Should I just only adjust it as -g_const*rho inside the inner cylinder?

Thank you again for your time.

Best regards
Razieh

Hi,

Yes, outside cylinder should also include buoyancy force because hot fluid is cooling down at near walls and due to this there is volume force directed downwards.

Solving this could be difficult so try finer mesh and give some small initial values for flow speed (y-direction).

Best regards

Tero