# Modelling large number of large lenght tubes using periodic interface

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 December 7, 2011, 05:39 Modelling large number of large lenght tubes using periodic interface #1 Member   DB Join Date: Apr 2011 Posts: 81 Rep Power: 8 Hi All, I need to model a system which is connected to a heat exchanger ahving 990 tubes of 2m length each. I know periodic interfaces can be used to simulate the pressure drop across the tube. Since the mass flow is to be predicted; which would depend on the pressure drop across the tubes I need to simulate them properly. I need to know how can it be done using translational periodic interfaces and simulating only a small length of the tubes instead of entire 2m. Please Help !! __________________ -D.B

 December 7, 2011, 18:20 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,194 Rep Power: 109 Should work with periodic interfaces. Define a pressure loss condition according to the pipe friction equation and it should work fine.

 December 8, 2011, 06:12 #3 Member   DB Join Date: Apr 2011 Posts: 81 Rep Power: 8 Thanks for the reply. But why do we need to specify the pressure drop ? doesnt CFX, based on the calculation in that small domain get the pressure drop. Also I need a Static Pressure outlet condition. How do I ensure that this condition is ensured. __________________ -D.B

 December 8, 2011, 06:38 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,194 Rep Power: 109 Looks like I have misunderstood what you are trying to do. Can you draw a picture of it and describe what you intend doing?

December 8, 2011, 06:58
#5
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DB
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Hi Glenn,
I have attached the line diagram of my case. I want to predict the flow in the system where a fan is attached. So I need to simulate the entire system along with the HE. The HE inlet is important and flow loss due to flow striking at the HE inlet is important so it is imperatibe that I model the HE inlet and the tubes as well.

Instead of modelling the entire 2m of tube length I want to model only a small length of the tube. The BC at tube Exit ( OUT) is atmospheric Static pressure and BC at inlet is total Pressure inlet.
Attached Images
 Diagram.JPG (14.0 KB, 22 views)
__________________
-D.B

 December 8, 2011, 07:12 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,194 Rep Power: 109 Where is the fan attached? How does the HE affect the flow? Where are the 2m long pipes? Your diagram is not very clear.

 December 12, 2011, 00:14 #7 Member   DB Join Date: Apr 2011 Posts: 81 Rep Power: 8 Hi Glenn, The rectangle where 'HE' is marked is the location of the tubes. The H.E affects the flow by virtue of its presence and flow area blockage ( which is huge ) The fan is located at the 90 degree turn after the inlet. It is a radial fan throwing air in the upward direction. __________________ -D.B

 December 12, 2011, 19:56 #8 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,194 Rep Power: 109 Can you post an image of the domains from CFX-Pre, and label the regions? Your diagram does not explain much.

 December 21, 2011, 23:56 #9 Member   DB Join Date: Apr 2011 Posts: 81 Rep Power: 8 Sorry for the late reply, I will do that soon. But by the time I would like to ask you something..My system had nothing to do with my doubt..irrespective of the system configuration I just want to know how to simulate a heat exchanger with vary large number of tubes of long length where it is a part of the system by using translational periodicity. __________________ -D.B

 December 22, 2011, 03:08 #10 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,194 Rep Power: 109 Again, need a diagram. Which direction is the hot and cold fluid flowing? Any cooling fins or other features?

December 22, 2011, 06:16
#11
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DB
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Hi,
Here is the Diagram Attached. The box on left had side is the H.E. and the cold fluid is the one shown by arrows. Actually I am not doing a Heat Transfer Simulation at all..This is purely a flow simulation of the cold side fluid system
Attached Images
 Diagram.JPG (17.7 KB, 10 views)
__________________
-D.B

 December 22, 2011, 07:30 #12 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 14,194 Rep Power: 109 Does the heat exchanger have pipes? Where are they? What direction do they run?

 December 23, 2011, 06:45 #13 Member   DB Join Date: Apr 2011 Posts: 81 Rep Power: 8 Hi Glenn, Yes there are tubes, as I said earlier I am interested in the effect of tubes on the flow. The tubes are in the box named H.E. going from right to Left in the figure. __________________ -D.B

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