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heat exchanger with perforated fins ... help

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Old   April 18, 2014, 12:36
Unhappy heat exchanger with perforated fins ... help
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Hi
I have cross flow finned tube heat exchanger with perforated annular fins as shown below.
http://s10.postimg.org/hhq4dfxih/Sna...BIT_Solver.png

after finishing the mesh and geometry and applied boundary condition by using GAMBIT i had exporting the case to fluent.
the problem, there is no connection between the duct and heat exchanger, in the other word the air doesn't collide with finned tube, so there is no stagnation and heat transfer.
Notes
1- constant temp. B.C applied to inner diameter of the pipe
2- the true result must be as shown in fig. below
http://s10.postimg.org/w9uu4s3ft/perforated_fin.jpg
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Old   April 21, 2014, 08:04
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Really need help
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Old   April 21, 2014, 22:37
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Sounds like you didn't subtract the inner part from the outer enclosure. Gambit won't automatically subtract the two in a boolean manner just because you set the boundary conditions appropriately. I would check your order of operations or, worst-case, post your journal file for us to review.

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Old   April 22, 2014, 09:21
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thank u for your reply
subtract doesn't used here because i have no smooth pipe. I thing split volume must be used in my case. I used volume option to split the two volumes, Bidirectional and
connected options were selected, Retain option was unselected. is this right way please?
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Old   April 22, 2014, 13:14
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You need a Solid volume part and a FLUID volume. You need to ask how to do that in the meshing and the geometry section under the GAMBIT section.
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Old   April 22, 2014, 13:28
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thank u for your reply
right
I do that, but there is no connection between (fluid and solid) volumes
I think the true result gained by use true method to split the two volumes.
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Old   April 22, 2014, 13:36
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of course between SOLID and FLUID, you need walls. I have no idea how to setup a mesh using GAMBIT... I wish i could help more
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Old   April 22, 2014, 13:42
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Never mind, thank u so much
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Old   April 28, 2014, 01:36
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Quote:
Originally Posted by ayad View Post
the problem, there is no connection between the duct and heat exchanger, in the other word the air doesn't collide with finned tube, so there is no stagnation and heat transfer.
Notes
1- constant temp. B.C applied to inner diameter of the pipe
2- the true result must be as shown in fig. below
http://s10.postimg.org/w9uu4s3ft/perforated_fin.jpg
can you post a picture of your problem for comparing with your perforated_fin.jpg
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Old   April 28, 2014, 03:02
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Hi max thank u for your reply


As you see there is no temp. variation in the air temp.
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Old   April 28, 2014, 03:06
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I never did such computation, but I assume you have to handle thermal conduction within thin wall
check here:
https://www.sharcnet.ca/Software/Flu...e253.htm#33023
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Old   April 28, 2014, 03:28
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Indeed i have select the Coupled option B.C. in the fluent .
I think the problem in the gambit, because there is no connection between the pipe and the duct. any method make a stagnation between fins and air will be solve the problem.
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Old   April 28, 2014, 03:38
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do you have "shadow" walls?
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Old   April 28, 2014, 03:41
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Yes, I have.
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Old   April 28, 2014, 03:46
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are you coupling the good surface with its shadow surface?
if I see your picture you at least need 5 coupling
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Old   April 28, 2014, 03:51
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No, I didn't do that.
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Old   April 28, 2014, 03:54
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then what did you do?
display the list of your bc (wall and shadow) and explain what you did
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Old   April 28, 2014, 04:19
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firstly i specified two zones fluid zone (duct), and solid zone (pipe and fin).
then,
inter: fin surface area (coupled B.C.)
P: duct outlet (pressure outlet B.C)
S: Inner diam. of the pipe (constant temp. B.C.)
V: duct inlet (velocity inlet B.C)
WS: 4 wall of the duct
wall: I dont know why is appear
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Old   April 28, 2014, 04:27
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*wall contains all outer surfaces on which you didn't set any BC, and Gambit set them automatically as wall

ok, now display the BC on inter and inter:012
and show me its geometry
(how did you set the BC? did you pick inter and inter:012 or only inter, then inter:012?)
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Old   April 28, 2014, 04:47
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thank you for your time,and I'm sorry for delay, there is a problem in fluent because i connect the computer with internet, So i can't take a picture.
But, the fin and pipe surface area are the geometry of inter.
only inter gave B.C (coupled), and i had neglect inter:012.
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