
[Sponsors] 
May 5, 2003, 08:14 
Mass Flow Rate Conservation Problem

#1 
Guest
Posts: n/a

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, 09:45 
Re: Mass Flow Rate Conservation Problem

#2 
Guest
Posts: n/a

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, 10:03 
Re: Mass Flow Rate Conservation Problem

#3 
Guest
Posts: n/a

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, 10:11 
Re: Mass Flow Rate Conservation Problem

#4 
Guest
Posts: n/a

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, 10:15 
Re: Mass Flow Rate Conservation Problem

#5 
Guest
Posts: n/a

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, 10:26 
Re: Mass Flow Rate Conservation Problem

#6 
Guest
Posts: n/a

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


May 5, 2003, 10:32 
Re: Mass Flow Rate Conservation Problem

#7 
Guest
Posts: n/a

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, 11:39 
Re: Mass Flow Rate Conservation Problem

#8 
Guest
Posts: n/a

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, 11:43 
Re: Mass Flow Rate Conservation Problem

#9 
Guest
Posts: n/a

thank you !!


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Mass flow rate through each cell  Babakjingo  Main CFD Forum  0  August 21, 2011 03:18 
Mass Flow Rate Error  jallison  FLUENT  1  May 16, 2011 16:22 
I have a problem with the sign of mass flow rate Enthalpy  behrang2009  FLUENT  0  June 6, 2010 18:02 
mass flow in is not equal to mass flow out  saii  CFX  2  September 18, 2009 08:07 
Determine mass flow rate along flow path  Atit Koonsrisuk  CFX  2  October 5, 2003 04:47 