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Mass convergence within heat exchangers

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Old   August 3, 2021, 03:46
Default Mass convergence within heat exchangers
Join Date: Jan 2018
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Hello all,
I have a toy example for heat exchanger where I am testing for different configurations to later create a lower fidelity simulation.
The concern here is that althouth the flow through manifold inlet and manifold outlet conserves, the flow through tube-inlets and tube outlets doesnt! The result is shown below, where entrysection_i and exitsection_i indicate sections at tube inlets and tube outlets respectively.

entrysection1 0.00034643523
entrysection2 0.0003462541
entrysection3 0.00035063147
entrysection4 0.00034650993

exitsection1 0.00035752518
exitsection2 0.00035785544
exitsection3 0.00035796402
exitsection4 0.00035505854
inlet_inmanifold:21 0.00144
outlet_outmanifold:20 -0.0014399984

One can observe that entry1 and exit1 does not match. Same goes for other 3 sections.
Could someone point out, what could be the reason for this mis match?
I have tried suggesting that this is due to fluid remaining within the manifolds, which leads to this difference in the mass flow rate within tube inlets and tube outlets, but apparently, I have been told, that flow in should match the flow out within the tube as well.
Any pointers?
The flow is turbulent (RE>3500), with standard k-epsilon model.
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File Type: jpg mesh2.jpg (84.1 KB, 6 views)
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mass conservation, mass flow rate

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