[chriss85]

Hello,

I would like to use the wideBandAbsorptionEmissionModel (actually, a modified version with tabular data instead). However, it is not clear to me what the EhrrCoeff parameter is, and the comments in the source do not make it clear to me.

There are also no examples that use this model unfortunately.

Can anyone help me out on this?

[Yuri Almeida]

Hi Chriss,

There is a comment in the OF 1.7:

"Proportionality constant (EhrrCoeff*HRR) to be emitted. Source term in RTE"

I'm not sure about it, but, considering that you are working with combustion, I think that is correlated with some kind of photon emission during the appearance of free radicals within the flame, that currently is not modeled (I think that you are using a single step reaction, right?).

This term may be trying to take into account these effects... I'd choose the value of 0 (zero), unless you are sure about the exact meaning of it.

But I'm just guessing, maybe someone with more experience can explain better to us...

Best,

[chriss85]

Thanks, that helps a bit.

I'm working on plasmas, so no combustions/flames, just a very high temperature one-fluid plasma without chemical reactions.

Similar question, is the E coefficient in constantAbsorptionEmission similar?

Also, in which cases is the emissivity inequal to absorptivity?

As far as I know they should be equal in thermal equilibrium (atleast in the P1 model). The equations I've seen are the same as those in OpenFOAM, but they use the absorptivity parameter everywhere since they assume e=a.

[Yuri Almeida]

I'm not really sure, but I agree with you.

Looking at the absorptionEmissionModel.H:

// Emission contribution

//- Emission contribution (net)
virtual tmp<volScalarField> E(const label bandI = 0) const;

//- Emission contribution for continuous phase
virtual tmp<volScalarField> ECont(const label bandI = 0) const;

//- Emission contribution for dispersed phase
virtual tmp<volScalarField> EDisp(const label bandI = 0) const;


Apparently, the constant E provides the similar effect as EhrrCoeff.

I don't remember a case in which we have different absorption and emission coefficients. According to Modest, at least for gases, equation 10.16 shows that they must be equal. Maybe the OpenFOAM provides the option to set a different value for each coefficient just in case of new developments, perhaps in solids...

For the wideBandAbsorptionEmission and the greyMeanAbsorptionEmission, we just provide the coefficients to obtain the absorption coefficient, and then it's set up equal to the emission coeff (e=a).

[sebastien_F1]

Ehrcoeff is used in fire application when you know the global radiant fraction from the experiment for a given fuel.
It can also be used for applciations in LES when you underestimate the true temperature and you want to account for it by adding an extra emission term in your RTE.

Otherwise, I was wondering if you know the units of bandLimits?

Thanks
Sebastien

[Yuri Almeida]

I think it is metre [m].

The wideBandAbsorptionEmission.H provides the example of "bandLimits (1.0e-6 2.63e-6);"

If 1.0e-6 is in metre, the band Limits would be 1 to 2.63 micrometres. I am not quite sure if it is a good estimative for the absorption bands of CO2 and H2O, but I think it is OK.

[atulkjoy]

EhrrCoeff givew radiant fraction of a flame mainly gives Qr/Qchem where Qr is heat release rate by radiation while Qch = Heat release rate by Chemistry or combustion as Qc = mdot*Hf for a fuel Hf is heat of combustion with mdot as mass flow rate.
Radiant fraction*HRR provides additional source term in RTE some more Amount of Energy to be emitted.
I am not conformed but it can be a result of TRI(Turbulence and radiation Interaction). One thing is for sure it will bring down flame temperature more normal RTE solution without Soot or out scattering.
Please check with
Ankur Gupta Thesis of PSU , M. Modest

[battiston]

Hello everyone,


I'm trying to implement BC wideBand in my case, but it always presents an error stating that specie ft was not found, could someone help me to implement this condition?

OF v2006
Rad model = fvDOM


Att,
Lucas L. Battiston

[battiston]

Originally Posted by battiston

Hello everyone,


I'm trying to implement BC wideBand in my case, but it always presents an error stating that specie ft was not found, could someone help me to implement this condition?

OF v2006
Rad model = fvDOM


Att,
Lucas L. Battiston

Hello everyone,


I managed to run, it's working now but this error appears:

#0 Foam::error:rintStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in /lib/x86_64-linux-gnu/libpthread.so.0
#3 Foam::divide(Foam::Field<double>&, Foam::UList<double> const&, Foam::UList<double> const&) at ??:?
#4 Foam:perator/(Foam::tmp<Foam::Field<double> > const&, Foam::tmp<Foam::Field<double> > const&) at ??:?
#5 ? in ~/OpenFOAM/OpenFOAM-v2006/platforms/linux64GccDPInt32Opt/bin/buoyantPimpleFoam
#6 ? in ~/OpenFOAM/OpenFOAM-v2006/platforms/linux64GccDPInt32Opt/bin/buoyantPimpleFoam
#7 __libc_start_main in /lib/x86_64-linux-gnu/libc.so.6
#8 ? in ~/OpenFOAM/OpenFOAM-v2006/platforms/linux64GccDPInt32Opt/bin/buoyantPimpleFoam


Can anyone help?



att,
Battiston

[B_R_Khan]

Originally Posted by Yuri Almeida

I think it is metre [m].

The wideBandAbsorptionEmission.H provides the example of "bandLimits (1.0e-6 2.63e-6);"

If 1.0e-6 is in metre, the band Limits would be 1 to 2.63 micrometres. I am not quite sure if it is a good estimative for the absorption bands of CO2 and H2O, but I think it is OK.

Hi!

Do you know if these band limits are the range of wavelengths we want to know intensity of radiations in or are they specific to each specie? For example can I set a range of 100nm to 200nm for CO2, H2O etc? and what does the word band actually mean I am quite confused. Does it mean IR, UV bands etc or just any custom defined group of wavelengths?
Please help!

Thanks