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Old   May 13, 2008, 09:52
Default Troubles with heat release rate
  #1
Xavier Ponticq
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Hi all,

I'm modelling an heptane pool fire in a tunnel by an inlet with a fixed mass flow rate of heptane. This mass flow rate is fitted to reproduce a 750 kW burner in complete combustion conditions.

When I post-treat my runs, I compute the heat release rate using the O2 consumption method widely used in experiments. I obtain heat release rate way above the imposed value (around 970 kW). I'm using the Eddy Dissipation Model with a custom single-step reaction for heptane, with a SST turbulence model in steady state.

I cannot understand why the calculated heat release rate is above the theoretical heat release rate imposed at the inlet. So if you, folks, have any idea about that, I'll be interested.

Regards
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Old   September 12, 2012, 11:59
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Michael
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Hi Xavier,

most probably it is the same problem as described here eddy dissipation concept + infinitely fast chemistry

You calculated the convective part of the fuel inlet flow, but there is also a diffusive. I will reply in the above mentioned thread if I find a solution.

Cheers,

Michael
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Old   September 12, 2012, 13:06
Default About installation of swak4Foam
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M Mallikarjuna Reddy
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Hi everyone,
I am fresher for openFoam. I came to know the uses of swak4Foam utility. But i am not able to install swak4Foam. I followed each and every step correctly but, got the following error message.

Error Message:-

malli_reddy@ubuntu:~/OpenFOAM/malli_reddy-2.1.1$ svn checkout https://openfoam-extend.svn.sourcefo...ies/swak4Foam/

svn: OPTIONS of 'https://openfoam-extend.svn.sourcefo...ries/swak4Foam': Could not resolve hostname `openfoam-extend.svn.sourceforge.net': No address associated with hostname (https://openfoam-extend.svn.sourceforge.net)

Please help me to overcome this problem. Now iam using OF 2.1.1 version.

Thanks
Regards
Mallikarjuna
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Old   September 12, 2012, 15:25
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Talita Possamai
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Quote:
Originally Posted by Xavier Ponticq
;87929
Hi all,

I'm modelling an heptane pool fire in a tunnel by an inlet with a fixed mass flow rate of heptane. This mass flow rate is fitted to reproduce a 750 kW burner in complete combustion conditions.

When I post-treat my runs, I compute the heat release rate using the O2 consumption method widely used in experiments. I obtain heat release rate way above the imposed value (around 970 kW). I'm using the Eddy Dissipation Model with a custom single-step reaction for heptane, with a SST turbulence model in steady state.

I cannot understand why the calculated heat release rate is above the theoretical heat release rate imposed at the inlet. So if you, folks, have any idea about that, I'll be interested.

Regards
Hello Xavier,

As I see it, a few theoretical definitions are needed here:

The heat release rate is by definition the energy released in the combustion process and it is related only to the mass of burned fuel.

So, if you are sure you are injecting exactly the fuel mass to release 750 kW and you are injecting enough O2 to burn all the fuel than you should have exactly 750 kW. If you don't have it than the problem is probably one of the following:

1 - Your simulation is not fully converged;
2 - Your inlet fuel mass flow is not correct (you can check it in the Post).
3 - You are calculating your heat release rate wrong.

To calculate exactly the energy release you must use the Enthalpy per [mol] of reaction at reference condition given by CFX for your reaction. It can by seen in the Solver under Single Step Reactions Heat Release.

The O2 comsuption method is as you said used in experimental analysis. In numerical analysis you must use the same reference as the numerical model.

Regards,
Possa.
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Old   September 12, 2012, 18:49
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This is the CFX forum. For questions on openfoam try here: http://www.cfd-online.com/Forums/openfoam/

And don't hijack other threads please, start a new thread for a new question.
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