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Setting up heat transfer between Pipe and the Fluid within

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Old   December 21, 2022, 20:58
Question Setting up heat transfer between Pipe and the Fluid within
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Hello,

I'm trying to set up a simulation where a fluid flowing through a pipe is being heated from outside the pipe (heat exchanger research project).

I've set it up so that the pipe is a solid with the outer wall's thermal specification set to 'Temperature' at 60C and the inner wall's thermal specification is set to 'Convection'. The thermal specification at the fluid/pipe interface is 'Conjugate Heat Transfer', energy source option is at currently at 'None' but I don't know if that is correct. Any alternate ideas on setting up the simulation for my use case are also welcome, this is just what I thought would work.

Fluid and solid models are shown in the image attached, both have energy models and I've chosen steady for now, but it will be an unsteady simulation in the end. The other photo shows that while the solid is 333K as expected, the fluid isn't heating up as a result but staying a constant 300K.



I'm new to CFD in general and this is my first time using it outside of tutorials so any help is much appreciated.


Thank you and Happy Holidays!
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File Type: jpg simulation2.jpg (90.5 KB, 23 views)
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Old   December 22, 2022, 02:39
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What you want is an interface between the two regions (solid and fluid). Then heat transfer is handled automatically by the software. When you specify "Convection" as a boundary condition on the pipe inner wall like you did, it means you must manually specify a heat transfer coefficient and ambient temperature. This would be the approach if you don't want to model the fluid flow (so a solid-only model) and instead look up an approximate HTC from literature (e.g. from Nusselt number correlations).
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Old   December 22, 2022, 19:01
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Hi, thank you for your reply.

In the second image, I have the Fluid/Pipe interface with the thermal specification set to 'Conjugate Heat Transfer'. Is there something I need to change with regards to this interfaces' settings? I read elsewhere that since the interface exists, setting the inner wall to 'convection' is irrelevant since the interface conditions supersede it anyway.

I also tried removing the solid pipe entirely and simply specifying the thermal condition of the fluid wall to 60C but couldn't get that to work either, the fluid was just constant at room temperature throughout.

I'm basically just trying to heat a fluid from the outside as it moves through a tube but can't seem to figure it out.

Thank you again.
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Old   December 23, 2022, 03:21
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Sorry I didn't notice you already had an interface defined.

Quote:
I read elsewhere that since the interface exists, setting the inner wall to 'convection' is irrelevant since the interface conditions supersede it anyway.
Yes that is true. Are you sure there is exactly zero heat transfer across the interface? It may be that if the pipe is short and fluid velocity high, the heat up of the fluid will be pretty low. Did you measure the heat transfer with a report to verify it is precisely zero? If yes then there is likely a problem with the interface definition.
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heat exchanger model, heat transfer modelling, turbulent flow in tube

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