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May 5, 2003, 09:14 
Mass Flow Rate Conservation Problem

#1 
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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 MassFlow rate (specified with massflowinlet 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. 

May 5, 2003, 10:45 
Re: Mass Flow Rate Conservation Problem

#2 
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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. 

May 5, 2003, 11:03 
Re: Mass Flow Rate Conservation Problem

#3 
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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. 

May 5, 2003, 11:11 
Re: Mass Flow Rate Conservation Problem

#4 
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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 

May 5, 2003, 11:15 
Re: Mass Flow Rate Conservation Problem

#5 
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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. 

May 5, 2003, 11:26 
Re: Mass Flow Rate Conservation Problem

#6 
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Does FLUENT tells you that you have inverted flow on some cell at the outlet?


May 5, 2003, 11:32 
Re: Mass Flow Rate Conservation Problem

#7 
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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.e03 velocity residual : 1.e03 energy (thermal model): a little more than 1e03 

May 5, 2003, 12:39 
Re: Mass Flow Rate Conservation Problem

#8 
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Try to do more iterations. If residuals of energy is over 1e6, 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. 

May 5, 2003, 12:43 
Re: Mass Flow Rate Conservation Problem

#9 
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thank you !!


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