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Hot water tank - help me please :)

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Old   January 13, 2007, 09:12
Default Hot water tank - help me please :)
  #1
Anthony
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Hi everyone, my hot water tank has two inlets (one hot, one cold) with "mass-flow inlet" conditions and one outlet with "pressure outlet" condition. When i'm doing the simulation, Fluent says that there is a reversed flow on the outlet and don't even display the residuals but when I use "velocity inlet" conditions instead, everything is ok. The thing is I can't use "velocity inlet" conditions in my case because free convection has a big effect in a water tank and so density must not be constant. Do you have any idea to help me out?

Thanks in advance for your answers
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Old   January 13, 2007, 11:43
Default Re: Hot water tank - help me please :)
  #2
Ralf Schmidt
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Hi!

Are you shure, that the direction of the mass flow inlet is correct? The "reversed flow" on the outlet might come due to a negativ mass flow on the inlet. Set the mass flow "normal to bondary"

Ralf
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Old   January 13, 2007, 11:55
Default Re: Hot water tank - help me please :)
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Anthony
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Hi Ralf, you were right, the mass flow was set "Direction Vector" and now that it's set "normal to boundary", everything's fine. I was stucked on this for several days so thank you very much for your answer!

Anthony
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Old   January 16, 2007, 10:46
Default Re: Hot water tank - help me please :)
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Venkatesh V
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Following are mu suggestions. 1. First make sure in real life also what you are experiancing in CFD is not happening.

2. Try to extend (extrude) the outlet for 3 or 4 diameters.( follow this strategy if you find some re-circulation near outlet) 3. Check the value of pressure at outlet. Assign correct value of operating pressure. Check the gravity direction.

Hope one of them should solve your problem

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Old   January 16, 2007, 13:40
Default Re: Hot water tank - help me please :)
  #5
Anthony
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Hi everyone, now that my boundary conditions problems are solved, I would like to simulate natural convection in my vertical hot water tank, which is adiabiatic, and I heard about Boussinesq approximation and density vs temperature fonction, which one should I use and how should I set it up?

I'm supposed to get a clear boundary between hot and cold water but everything i tried, gave me a mix between the two temperature. Actually, i'm supposed to do an unsteady simulation but as I don't really know unsteady model, I wanted to be sure that natural convection was really working in a steady case before trying unsteady.

Thank you very much for your help, I really appreciate.

Anthony
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