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Mixing Problem in Double Pipe Heat Exchanger With Fluid Fluid Interface

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Old   December 17, 2015, 07:38
Default Mixing Problem in Double Pipe Heat Exchanger With Fluid Fluid Interface
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Shomaz ul Haq
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Dear all,

Hi. Hope all are well. I am facing a problem in CFX Post. I am simulating a counter flow double pipe heat exchanger. Cold water enters inner pipe left side and hot water enters outer pipe right side. The thing is cold water entering from bottom is mixing and turning left towards outlet of hot pipe. This can be seen in the streamlines shown in attached file. Firstly, I want to ask why is the cold water mixing with the hot water even with the fluid fluid interface in between the domains? And secondly why isn't the cold water going any further along the length of the pipe towards cold water outlet? Doesn't a fluid fluid interface prevent mixing? In short no heat transfer is transferred along the major portion of the heat exchanger.
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Old   December 17, 2015, 07:57
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Maxim
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Hi, you should add the screenshots directly into your post. Not all of us have Microsoft Word or want to download a file from an unknown person from the internet...
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Old   December 17, 2015, 10:36
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Sorry Maxim. Of course. I'll attach the jpeg files.
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Old   December 17, 2015, 13:50
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Fluid Fluid interfaces do exactly that, connect one fluid domain with another fluid domain. By default the fluid is allowed to cross the interface.

However, if you activate an interface model for the fluid fluid interface, and force it to behave like a wall, you will get the behavior you were expecting.
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