[megacrout]

Hi everyone,

I am currently looking at the code behind combustion solvers, especially reactingFoam. I am interested in the way reversible reactions are implemented. I figured out that the reaction rate of the backward reaction is computed using the equilibrium constant K which is computed as

K = exp( - nMoles * g(T) / (RR * T) )

where the gibbs enthalpy is in turn computed as

g(T) = h(T) - T*s(T).

This means

K = exp ( - nMoles * (h(T) - T*s(T)) / (RR*T) )

where RR represents the reaction rate. This does not seem very close to

K = exp ( - (h(T) - T*s(T)) / (R*T) )
´
where R is the gas constant, which is supposed to be the correct expression for the equilibrium constant (right ?).

Futhermore, I just CANT find in the online C++ documentation where cp(T), h(T) and s(T) are computed. I know that it is based on the Janaf parameters from which the heat capacity is also derived (http://cea.grc.nasa.gov/def_formats.htm). But I cannot find where this computation is being done, where the equation is implemented! And since all other thermophysical parameters are then derived from those three (as mentioned in the header of specieThermo.H for example), I really want to know where to find those equations in OF.

This is not the first time I spend a few hours looking for a specific equation so that´d be a really great help if you can give me an answer. Even just a hint ahah!!

thx!

Tibo

[Chris Lucas]

Hi,

I'm not sure what you want to know?

The specific values for cp ... are calculated in specieThermo using the molar values.

The molar values are calculated (depending in the model you use) e.g. in hConst or hPolynomial or janaf ...

Best Regards,
Christian

[megacrout]

Hi Chris,

Thanks for your answer.
I´m trying to know how cp(T), h(T) and s(T) are computed (files AND formulas)? I can´t see what you mentioned: specieThermo contains the formulas for computing all thermophysicals parameters BUT the three I´m looking for. Or I did miss something.
Where is - in the case of cp - the function hConst/hPolynomial/janaf being called? I did not find it in specieThermo (I must admit I´m a C++ newbie, though).

As I mentioned, it is not the first time I get lost in the C++ documentation of OpenFOAM and in specieThermo is another good example: where is the parameter W() computed? It is used in ThermoI.H but I can´t find where its formula lies or even where it is being called.

Best regards,

Tibo

[adhiraj]

I think it was janafthermo.

[Chris Lucas]

Hi

for W() have a look at the files in

$FOAM/src/thermophysicalModels/specie/specie

for cp, h ... look at

$FOAM/src/thermophysicalModels/specie/thermo/hConst

$FOAM/src/thermophysicalModels/specie/thermo/janaf

...

Best Regards,
Christian

[megacrout]

Hey Christian,

Thanks A LOT for the hints. I say "hints" because I´ve had to look for more details quite a long time before I could get what you mean.

The missing link were the files hsCombustionThermos.C and newhsCombustionThermo.C (which seems to have been renamed hsCombustionThermoNew.C in OF 2.0.1). Without the former file, there is no link between solver reactingFoam and the files specie or janaf/hConst/etc...

Now, I have a few more questions for you, I would greatly appreciate if you can further help me:
1) reactingFoam relies on the psiChemistrymodel (s. createFields.H), can one of the other models (rho, ODE, basic) be used as an option (i.e. without modifying the solver´s code)?
2) same question about hsCombustionThermo (s. createFields.H): could hCombustionModel, hhuCombustionModel or mixtureThermos be used instead, without altering reactingFoam´s structure, i.e. as an option?
3) Because reactingFoam relies on psiChemistrymodel and hsCombustionThermo, only 2 options can be given as thermoType in thermophysicalProperties:

hsPsiMixtureThermo<multiComponentMixture<gasThermo Physics>>
or
hsPsiMixtureThermo<reactingMixture<gasThermoPhysic s>>

and only 2 options can be given as psiChemistryModel in chemistryProperties:

ODEChemistryModel<gasThermoPhysics>
or
ODEChemistryModel<icoPoly8ThermoPhysics>

Is that right? If not, how can I implement another thermoType? Any attempt gave me error messages such as

"Inconsistent thermo package selected..."
or
"Unknown hsCombustionThermo type...""
4) If what I just wrote is right, then I still don´t see where hConst/specieThermo/janaf is called.

Finally, regarding my first post (still unanswered concerning reactions): I figured out in the meanwhile that RR is used for both reacting rate and gas constant depending on the file it is used in. However, I still do not get why nMoles appears in the mentioned equation. Can you help me?

Thx.

Tibo

[megacrout]

Anyone?
"Pretty please with sugar on top." (Harvey Keitel as Winston Wolf in Pulp Fiction)