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Old   August 11, 2003, 11:41
Default heat transfer flux
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Mark
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Hi,

I have simulated a combustion gas flow in a furnace. The heat transfer rate report from the flux reports gives me a Negative value at the inlet indicating heat leaving the domain at the inlet and positive value at the outlet - indicating heat into the domain. This can't be right!!!

The only thing I think of, were there might be a problem is that I used an outlet profile from a previous simulation as the inlet boundary condition for this simulation. Could this be causing a problem?

Everything else looks fine.

Thanks for your help

Mark
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Old   August 11, 2003, 20:55
Default Re: heat transfer flux
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Jin-Wook LEE
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I guess that your combustion model is mixture-fraction/PDF model. Is it so ? Then it is possible. For example, let your fuel be CH4. Then, standard enthalpy of formation of fuel(CH4) and products(CO2 and H2O) are negative. Then, numerically, negative flux to the fuel inlet and positive flux at the outlet.

Sincerely, Jinwook

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Old   August 12, 2003, 04:18
Default Re: heat transfer flux
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Mark
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Jinwook,

Thanks for your advice.

The combustion model I'm using is the eddy dissipiation. I should be using the PDF model but I wanted to used the eddy dissipiation model.

Is the advice the same for the eddy dissipiation model?

Regards,

Mark
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Old   August 13, 2003, 01:42
Default Re: heat transfer flux
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Jin-Wook LEE
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YES...................

Negative or positive heat flux to the 'outlet' and/or to the 'inlet' is entirely dependent of the value of the 'standard state of enthalpy(let SSE)', not dependent of the combustion model.

For your reference, I would like to introduce my idea.

I am using my own SSE values, to avoid confusing and to easily check the heat balance. They are,

SSE of N2=0, O2=0, CO2=0, H2O=0....... SSE of fuel=LHV(positive value) SSE of CO=LHV(positive value) (for two step model).

Then you can avoid the confusing and you can get positve at the inlet and negative at the outlet. The above approach is NOT valid if you are considering backward reaction. Note that SSE is used to calculate the reaction rate of backward reaction.

SIncerely, Jinwook
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Old   August 13, 2003, 01:49
Default Re: heat transfer flux
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Jin-Wook LEE
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Simply speaking, non-zero SSE for fuel only for single step model, and non-zero SSE for CO or other intermediate species for multi-step model.

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