[Ziwu]

Hey, all,

Recently, I was working on Coal Combustion submodels's modification and test.

I have two questions :
(1)about the values of parameters in the models, that where do these data come from?
(2)about the correction of the model description in COxidationKineticDiffusionLimitedRate Model compared with the original theoretical paper.

*************************************** Question (1) Start*****************************************
For example, under the path:
OpenFOAM-2.4.x/src/lagrangian/coalCombustion/submodels/sur
faceReactionModel/COxidationDiffusionLimitedRate/COxidationKineticDiffusionLimitedRate.C
================================================== =================
SurfaceReactionModel<CloudType>(dict, owner, typeName),
Sb_(readScalar(this->coeffDict().lookup("Sb"))),
C1_(readScalar(this->coeffDict().lookup("C1"))),
C2_(readScalar(this->coeffDict().lookup("C2"))),
E_(readScalar(this->coeffDict().lookup("E"))),
...
...
// Diffusion rate coefficient
const scalar D0 = C1_/d*pow(0.5*(T + Tc), 0.75);

// Kinetic rate
const scalar Rk = C2_*exp(-E_/(specie::RR*Tc));

// Particle surface area
const scalar Ap = constant::mathematical:i*sqr(d);

// Change in C mass [kg]
scalar dmC = Ap*rhoc*specie::RR*Tc*YO2/WO2_*D0*Rk/(D0 + Rk)*dt;
================================================== =================

And then under the path:
OpenFOAM-2.4.x/tutorials/lagrangian/coalChemistryFoam/simp
lifiedSiwek/constant/coalCloud1Properties
================================================== =================
COxidationKineticDiffusionLimitedRateCoeffs
{
Sb 1;
C1 5.0E-12;
C2 0.002;
E 7.9E+07;
}
================================================== =================
If you apply these data into the COxidationKineticDiffusionLimitedRate model,
with the carrier temperature Tc= 1250K, which is quite meaningful and realistic value, you will find immediately Kinetic rate Rk = C2_*exp(-E_/(specie::RR*Tc)) = 0,
C mass change rate dmC/dt=Ap*rhoc*specie::RR*Tc*YO2/WO2_*D0*Rk/(D0 + Rk) = 0,
which means under carrier temperature Tc=1250K, no carbon(I assume char contains 100% carbon) consumes at all.

Only if you specify carrier temperature Tc=50000K!!!!, you could get Kinetic rate Rk= 5.9e-86!!!! which means only under such high carrier(gas) temperatureTc=50000K could the carbon consume a litttttttttttttttle bit...

As you could understand why I confused a lot,
since the meaningful and realistic value Tc=1250K gives us Rk=0, no carbon consumes;
the unrealistic value Tc=50000K gives us Rk=5.9E-86, the carbon consume a litttttttttttttttle bit

what's the meaning of this COxidationKineticDiffusionLimitedRate model?
And what useful information could we get from these data "C2=0.002;E=7.9E+07;"
Especially the origin of values of model constants, these are the most suspected part!

*************************************** Question (1) End******************************************

*************************************** Question (2) Start*****************************************
The COxidationKineticDiffusionLimitedRate in OpenFoam relies on this paper:
"Predicting the Combustion Behaviour of Coal Particles" by M.M. BAUM and P.J. STREET.
If you could download and check the paper you will find in Page 237,
(Ignore "Surface factor Ψ" first...it's not important for now)
the chemical reaction rate K_CH ( which is the kinetic rate Rk in code) is the function of Tp (carbon temperature), but not the function of Tc (carrier temperature).

Did anyone notice these difference?
Should these difference still be existed in the code???????

*************************************** Question (2) End******************************************
I would appreciate anyone who could help me solving this question in advance!
THANKS A LOOOOOOT!