# Periodic Linear BC

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 September 20, 2016, 09:30 Periodic Linear BC #1 Member   Join Date: Sep 2016 Posts: 43 Rep Power: 9 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.

 September 20, 2016, 17:16 #2 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,665 Rep Power: 65 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

 September 20, 2016, 17:26 #3 Member   Join Date: Sep 2016 Posts: 43 Rep Power: 9 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?

 September 20, 2016, 22:31 #4 Senior Member   Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,665 Rep Power: 65 You need to make sure the mesh is matching (conformal) on both surfaces before you can make them periodic.

 September 21, 2016, 01:50 #5 Senior Member   Paritosh Vasava Join Date: Oct 2012 Location: Lappeenranta, Finland Posts: 732 Rep Power: 22 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

 September 21, 2016, 06:00 #6 Member   Join Date: Sep 2016 Posts: 43 Rep Power: 9 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

September 21, 2016, 16:43
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Quote:
 Originally Posted by LuckyTran 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?

 December 10, 2017, 09:38 #8 New Member   Caner Join Date: Jan 2010 Posts: 8 Rep Power: 16 Hello diggee Did you solve your problem about defining an input for periodic boundary condition?

 Tags boundary condition, linear, periodic