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Tube in Tube heat exchanger( But I got error)

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Old   September 24, 2008, 00:35
Default Tube in Tube heat exchanger( But I got error)
  #1
Young
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Dear all,

I have tried to simulate a heat exchanger.

Water is flowing at outer pipe and air is flowing at a inner pipe as following sectional diagram

---------------------------

water -->

--------------------------

air <--

---------------------------

water -->

---------------------------

I had two fluid domain (water, air) so I used "enable beta features (in option)" and turned off "constant domain physics" at simulation.

But I got error message like this

*********************************************** Global Statistics :

Global Number of Nodes = 31926

Global Number of Elements = 96078

Total Number of Tetrahedrons = 96078

Global Number of Faces = 58222

Minimum Orthogonality Angle [degrees] = 32.3 ok

Maximum Aspect Ratio = 6.4 OK

Maximum Mesh Expansion Factor = 21.8 !

Domain Interface Name : Domain Interface 1

Non-overlap area fraction on side 1 = 8.89E-06

Non-overlap area fraction on side 2 = 5.07E-08 ---------------------------------- Error in subroutine FNDVAR : Error finding variable DENSITY_FL1 GETVAR originally called by subroutine GET_MFLOIP_ZIF

+--------------------------------------------------------------------+ | Writing crash recovery file | +--------------------------------------------------------------------+ ---------------------------------- Error in subroutine FNDVAR : Error finding variable DENSITY_FL1 GETVAR originally called by subroutine GET_MFLOIP_ZIF

+--------------------------------------------------------------------+ | An error has occurred in cfx5solve: | | | | The ANSYS CFX solver exited with return code 1. No results file | | has been created. | +--------------------------------------------------------------------+

End of solution stage.

+--------------------------------------------------------------------+ | Warning! | | | | The ANSYS CFX Solver has written a crash recovery file. This file | | has been saved as F:\Thesis\prelim\test\001\model3_004.res.err and | | may be an aid to diagnosing the problem or restarting the run. | | More details should be available in the solver output section of | | the output file. Note that a lock file was left for the crash | | file when the solver exited, and so it is probably incomplete. | +--------------------------------------------------------------------+

+--------------------------------------------------------------------+ | The following user files have been saved in the directory | | F:\Thesis\prelim\test\001\model3_004: | | | | mon | +--------------------------------------------------------------------+

This run of the ANSYS CFX Solver has finished.

*************************************************

Would you let me know how I get over error?

and please share your exprience, if you have ever done this type heat exchanger.

Thanks have a great day
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Old   September 25, 2008, 19:36
Default Re: Tube in Tube heat exchanger( But I got error)
  #2
Glenn Horrocks
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Hi,

The first error says that is can't find the density for a material. Check that you have density defined for everything, or a sensible equation of state defined.

Glenn Horrocks
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Old   September 26, 2008, 01:35
Default Re: Tube in Tube heat exchanger( But I got error)
  #3
Young
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Dear Horrocks,

Thanks your response.

I use each fluid material as follows;

air = Air at 25C in CFX material library, its density is 1.185 kgm^-3 Water = water in CFX material library, 997 kgm^-3

However, it makes the same error message.

I suspect this issue is caused by interface condition.

But I don't know what makes errors.

I think it is simple crossflow heat exchanger between air tueb and water tube.

Have you ever run before?

Thanks

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