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Periodic Linear BC

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Old   September 20, 2016, 09:30
Default Periodic Linear BC
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Hello. I am modeling a corrugated plate heat exchanger. This is the isometric view of the complete 3 plate assembly. The red and blue region are the hot and cold channel, respectively with the three plates in-between them. This is better illustrated in this exploded view.

I want to impose conditions in fluent such that there is a cold channel above the topmost plate and a hot channel below the bottommost plate and so on effectively making it an assembly of infinite plates and channels. The sequence would look like '...-C-P-H-P-C-P-H-P-C-....' where C is cold channel, P is plate and H is hot channel. Can anyone please suggest as to how I should go about this?


Or I will be more then happy if someone can suggest a way that will make fluent treat the top most surface (top surface of the 1st plate) equivalent to the surface of the plate in contact with the cold channel (top surface of the 3rd plate) and similarly the bottom surface of the 3rd plate equivalent to the bottom surface of the first plate? By equivalent I mean that the temperature at those plate surfaces should be the same.



PS - I am sorry if the title is misleading, I do not know how to word this better.
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Old   September 20, 2016, 17:16
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Lucky Tran
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It looks like you just need to use a periodic boundary condition.
The TUI command is:
mesh/modify-zones> make-periodic

then follow the prompts
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Old   September 20, 2016, 17:26
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Yes I already did try that but it gives the following error

Warning: Number of elements does not match between zone 6 and 10.
Error: Failed to make zones periodic.
Error Object: #f

What does that mean?
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Old   September 20, 2016, 22:31
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You need to make sure the mesh is matching (conformal) on both surfaces before you can make them periodic.
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Old   September 21, 2016, 01:50
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Paritosh Vasava
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You can create an interface between both the surfaces and while doing so, select 'periodic'. Worth a try!

If it dosent then as LuckyTran suggested, you need matching/conformal mesh on both the surfaces.

Last edited by vasava; September 21, 2016 at 01:50. Reason: typo
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Old   September 21, 2016, 06:00
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Yes I know but the problem in trying to do that is that I have already combined all the parts into one body to get conformal meshing throughout and to avoid mesh interfaces. But since the top surface of the 3rd plate has the cold channel on top of it, its topology is now different from the top surface of the 1st plate which results in a non identical mesh on these two surfaces. I hope the two images below illustrate this better.

http://imgur.com/XRV5Qaz

http://imgur.com/3YFcQXC
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Old   September 21, 2016, 16:43
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Quote:
Originally Posted by LuckyTran View Post
You need to make sure the mesh is matching (conformal) on both surfaces before you can make them periodic.
Hey, I changed my setup slightly so that I could do this. I now have conformal meshes on the topmost and bottom most surface. I did make them periodic from the TUI and it was a success! Fluent went on to delete one of these surfaces then as it is supposed to do with periodic faces, I guess.

The problem now is that what do I give as input to the periodic boundary condition? There is certainly no mass flow as I have made the two solid plates periodic. Since there is no fluid flow through the plates but only conduction, I do not think that I can give a value for pressure gradient too. What about the values for the direction?
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