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Two Mass flow inlet bc convergence problem

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Old   December 12, 2015, 12:58
Default Two Mass flow inlet bc convergence problem
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Nabid Aunjum Hossain
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HI all! I am trying to simulate heat transfer problem in a double pipe heat exchanger in which i need to calculate the pressure difference in the inner fluid.

Materials : inner fluid: user defined nano fluid
outer fluid: hot water
inner tube: copper
outer tube: insulated

Now if I choose two different mass flow rate for the two inlet the solution is having very annoying convergence problem(reverse flow remain through out the simulation).But if i choose same mass flow rate for both the inlet solution converges .But i need to use to different mass flow rate for both the inlet

BC: Both inlet: Mass flow inlet(temp 298 and 318K)
BOth outlet : Outflow
Mesh :simple Mapped face meshing

Model: K epsilon standard and wall: standard

what might be the problem is it in mesh or in my bc or in the other physic setup.I can't get it even if i set mass flow rate for one inlet to 0.0789 and other inlet to 0.078 the residuals won't converge for at least first 800 iteration where if i choose 0.0789 for both the inlet it converges within first 200 iteration.

Plz help!!!!!

Last edited by nabidinhomessi; December 14, 2015 at 08:20.
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Old   December 12, 2015, 15:19
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Papiya Debi Ashru
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What is the difference between Bottom Boundary Layer and Benthic Boundary Layer?
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Old   December 13, 2015, 01:07
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Nabid Aunjum Hossain
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sorry can you elaborate? I have no idea about your question I am very much a beginner!
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Old   December 13, 2015, 15:25
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Papiya Debi Ashru
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Actually I'm also new comer.ould you please tell me how can I get proper answer through proper channel?
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Old   December 14, 2015, 01:27
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Hamid Zoka
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hi
how do you set the outlet boundary condition?
do you impose the same pressure level for both outlets?
If yes, this may be the reason. these channels have not necessarily the same pressure levels.

does it help?
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Old   December 14, 2015, 08:11
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Nabid Aunjum Hossain
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I set both the outlet boundary to outflow as i don't know the pressure at the outlet,actually i need to find the outlet pressure from the simulation.
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