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Old   May 5, 2003, 09:14
Default Mass Flow Rate Conservation Problem
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philippe
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Hello,

I simulate the flow of CO2 in a cylinder. After about 500 iterations, using Reports/Fluxes menu, I've got the good value of Mass-Flow rate (specified with mass-flow-inlet BC) i.e. 0.10 kg/s but I've got -0.10 kg/s at the outlet (defined as outflow BC) ! How can I solve this problem ?

Thanks.

Philippe.
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Old   May 5, 2003, 10:45
Default Re: Mass Flow Rate Conservation Problem
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ap
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Maybe I don't understand the problem: you have a cylindrical pipe and 0.10 kg/s of C02 entering it. FLUENT tells you that 0.10 kg/s enter the tube and -0.10 kg/s exit it. Right?

FLUENT considers negative all flows which exit the domain and positive all fluxes entering it. So the value you have at the outlet seems good.

Hi.
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Old   May 5, 2003, 11:03
Default Re: Mass Flow Rate Conservation Problem
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philippe
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Hi,

I think you understand my probleme: I have a negative mass flow rate on the surface which is the outlet of the whole 3D domain.

thank you.

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Old   May 5, 2003, 11:11
Default Re: Mass Flow Rate Conservation Problem
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ap
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Ok. As I've already told you, negative values of the mass flow rate at the outlet are not a problem.

Good work

Hi
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Old   May 5, 2003, 11:15
Default Re: Mass Flow Rate Conservation Problem
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philippe
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Hi I also have some negative values of static pressure at the outlet surface ?! I would like to be sure that the flow is computed in a good way.

Thanks.

philippe.
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Old   May 5, 2003, 11:26
Default Re: Mass Flow Rate Conservation Problem
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ap
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Does FLUENT tells you that you have inverted flow on some cell at the outlet?
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Old   May 5, 2003, 11:32
Default Re: Mass Flow Rate Conservation Problem
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philippe
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yes It tells that there is some reversed flows on 20/30 faces on the outlet surface. All the residuals are constant.

mass residuals less than 1.e-03 velocity residual : 1.e-03 energy (thermal model): a little more than 1e-03
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Old   May 5, 2003, 12:39
Default Re: Mass Flow Rate Conservation Problem
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ap
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Try to do more iterations. If residuals of energy is over 1e-6, your solution is not considered as a converged one by FLUENT.

Check all boundary conditions.

If you can, try to replace the Outflow boundary condition with a Pressure outlet (you need to know gauge pressure at the outlet). Read the manual about Outflow BC use for more info.

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Old   May 5, 2003, 12:43
Default Re: Mass Flow Rate Conservation Problem
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philippe
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thank you !!
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