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Temperature does not change in Fluent simulation

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Old   November 15, 2017, 06:39
Default Temperature does not change in Fluent simulation
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Hello,
I'm trying to simulate the heat transfer through a coil. I'm setting the heat transfer coefficient to 100 W/mēK and using a delta T of 20 K, but the temperatures barely change (you can also notice that the energy residuals don't change). However, using CFX solver with the same conditions, I get reasonable results.

Does anybody have any clue what could be wrong, please?

Boundary conditions:
Inlet:
velocity - 2 m/s
temperature - 298.15 K
Outlet:
gauge pressure - 0 Pa
Backflow temperature - 300 K
Walls:
no slip
thermal - check attached figure 1
(I've set no solid walls for simplicity)
1.png

residuals.png

Fluent.jpg

CFX.jpg
Attached figures: 1 - Wall thermal B.C.; 2 - Fluent residuals; 3 - Fluent post-processing; 4 - CFX post-processing.

Thanks in advance.
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Old   November 15, 2017, 19:59
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Alexander
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at inlet you have temperature - 298.15 K
at outlet temperature - 300 K

Fluent is trying to find solution according to your BC.
I have no idea why the temperature goes down in CFX, if you have the same BC there

You may try to use outflow BC in outlet

Best regards
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Old   November 16, 2017, 10:36
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Quote:
Originally Posted by AlexanderZ View Post
at inlet you have temperature - 298.15 K
at outlet temperature - 300 K
s
That's a backflow temperature (an inlet temperature when there is reversed flow). The 300 K is not a hard BC.

Quote:
Originally Posted by LThomes View Post
Does anybody have any clue what could be wrong, please?
It is a debugging problem I guess. Try using very stupid settings like 1000000 HTC.
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Old   November 16, 2017, 10:57
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Quote:
Originally Posted by AlexanderZ View Post
at inlet you have temperature - 298.15 K
at outlet temperature - 300 K
As LuckyTran said, 300 K is the backflow temperature at the outlet, it does not set the outlet temperature to a constant 300 K.

Thanks for the replies.
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