# Two Mass flow inlet bc convergence problem

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 December 12, 2015, 12:58 Two Mass flow inlet bc convergence problem #1 New Member   Nabid Aunjum Hossain Join Date: Nov 2015 Posts: 14 Rep Power: 10 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.

 December 12, 2015, 15:19 Bbl #2 New Member   Papiya Debi Ashru Join Date: Dec 2015 Posts: 2 Rep Power: 0 What is the difference between Bottom Boundary Layer and Benthic Boundary Layer?

 December 13, 2015, 01:07 #3 New Member   Nabid Aunjum Hossain Join Date: Nov 2015 Posts: 14 Rep Power: 10 sorry can you elaborate? I have no idea about your question I am very much a beginner!

 December 13, 2015, 15:25 Ask #4 New Member   Papiya Debi Ashru Join Date: Dec 2015 Posts: 2 Rep Power: 0 Actually I'm also new comer.ould you please tell me how can I get proper answer through proper channel? nabidinhomessi likes this.

 December 14, 2015, 01:27 #5 Senior Member   Hamid Zoka Join Date: Nov 2009 Posts: 282 Rep Power: 18 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? nabidinhomessi likes this.

 December 14, 2015, 08:11 #6 New Member   Nabid Aunjum Hossain Join Date: Nov 2015 Posts: 14 Rep Power: 10 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.

 Tags convergance, mass flow inlet, reverse flow

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