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-   -   Problems on H2/air CFX simulation (http://www.cfd-online.com/Forums/openfoam-solving/63600-problems-h2-air-cfx-simulation.html)

xulixian April 14, 2009 03:28

Problems on H2/air CFX simulation
 
am puzzled by the simulation of H2/air combustion using CFX. I could not get the expected temperature, the maximum flame temperature is always below 980K. I use stoichiometric mixture of hydrogen and air, but after the reaction, their always a lot of O2 left. It looks like a lean combustion. And the in the beginning of the simulation, CFX tell me
"
Reactants and products do not balance for a reaction.
| Products will not be scaled for conservation of mass. |
| |
| Reaction : Hydrogen Oxygen |
| Products scale = 2.7750
"
My reaction chamber is a tube with 0.2 mm in diameter and 1.55mm in length, the inlet diameter is 0.1mm. Adiabatic wall condition.The boundary is the following:

Inlet: 300K, 6 m/s, Mass fraction H2: 0.02857 O2: 0.22857 N2: constraint,

Outlet: static pressure 1 bar

Initial temperature: 1000K


I use the default stoichiometric coefficient, so the reaction is H2 + 0.5 O2 = H2O,

Pre-Exponential Factor : 3.12e7 [m^1.5 s^-1 mol^-0.5] **(the value in Fluent is 9.87e8, I change the value since I have to switch the uint from "kmol" in Fluent to "mol" in CFX.)
Temperature Exponent : 0
Activation Energy : 3.1e+04 j/mol.

In the begining of the simulation, I use the time step of 1 e-7 s, then I increase the time step to 1 e-5 s.

Can you help me to diagnose the simulation? I appreciate for your help.

kerstin April 14, 2009 14:29

Hi,
you should read the thread about wall heat flux in CFX answered by Bernhard.
;-)

Seems to become more and more people stumbling in the wrong forum. So we can start having fun now? ;-)

xulixian April 14, 2009 15:00

Hi Kerstin,
thank you for your reply. Acctually I proposed my question in CFX forum, but I didn't get any answers from them, so I tried my luck here, and it looks not bad! ^_^
I will check the thread you mentioned. thanks again.

regards, Lixian


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