[sega]

Hello World.

Can anybody tell me how I can access the partial pressure of a species / componente?
In my case I need the partial pressure of oxgen!

Cheers. S.

[vinaynitrkl]

i too need the same!

[gearboy]

Originally Posted by sega

Hello World.

Can anybody tell me how I can access the partial pressure of a species / componente?
In my case I need the partial pressure of oxgen!

Cheers. S.

You can use the following equation
pi=C_P(c,t)*gas_molar_fraction
where, pi is the partial pressure, C_P(c,t) gets the mixed gas pressure.
gas_molar_fraction is the mole fraction of a species in the mixture, which can be calculated by
- first summing up [mass fraction / molecular weight] of all species and
- then dividing the same quotient for the individual species by the calculated sum.
This is done automatically by the following function call (including variables and preparation):
Material *mix_mat = mixture_material(Get_Domain(1));
Material *spe_mat = NULL;
real all_mass_fracts[MAX_SPE_EQNS];
real all_mole_fracts[MAX_SPE_EQNS];
int i = -1;
mixture_species_loop(mix_mat, spe_mat, i)
{
all_mass_fracts[i] = C_YI(c,t,i);
}
Mole_Fraction(mix_mat, all_mass_fracts, all_mole_fracts)
After this, the mole fractions of all species can be found in the array "all_mole_fracts".

[sega]

Great, Thank you.

This leads me to the question to determine which position in the array corresponds to which species?

Any idea how I can know this?

[gearboy]

Originally Posted by sega

Great, Thank you.

This leads me to the question to determine which position in the array corresponds to which species?

Any idea how I can know this?

The index of the first species in the list of the Fluent interface is 0.
If the list in the Fluent is : O2, CO, CO2......, then
all_mass_fracts[0] means the mass fraction of O2, all_mass_fracts[1] means that of CO , and so on.

[sega]

Originally Posted by gearboy

The index of the first species in the list of the Fluent interface is 0.
If the list in the Fluent is : O2, CO, CO2......, then
all_mass_fracts[0] means the mass fraction of O2, all_mass_fracts[1] means that of CO , and so on.

Ok. I got this.
And how do I know the actual list?

[sega]

Ok. I put this so far into my code

    Material *mixtureMaterial = mixture_material(Get_Domain(1));
    Material *speciesMaterial = NULL;
    real massFractions[MAX_SPE_EQNS];
    real moleFractions[MAX_SPE_EQNS];
    real partialPressures[MAX_SPE_EQNS];
          
    int i = -1;
    mixture_species_loop(mixtureMaterial, speciesMaterial, i)
    {
        massFractions[i] = C_YI(cell,thread,i);
    }
    
    Mole_Fraction(mixtureMaterial, massFractions, moleFractions);
    
    int i = -1;
    mixture_species_loop(mixtureMaterial, speciesMaterial, i)
    {
        partialPressures[i] = C_P(cell,thread) * moleFractions[i];       
    }

Now the code is killing me. It want's a ; bevor the second int i = -1.
But there is one - right after Mole_Fraction( ... ).

So what may be wrong?

[Dr.Montazer]

Hi,

Well, as new member in OpenFoam (days of experience in OpenFoam) I would say using dsmcFoam (Direct simulation Monte Carlo (DSMC) solver for 3D, transient, multi- species flows) might help

Back in my Fluent experience, you have to use the Multiphase model and depends to the nature of component (mixture, Eulerian or VOF) will works fine. Looks the same approach is working in OpenFoam:

-compressibleInterFoam: Solver for 2 compressible, isothermal immiscible fluids using a VOF (volume of fluid) phase-fraction based interface capturing approach, )

More could be find at Standard solvers: http://www.openfoam.com/features/standard-solvers.php

[sega]

Originally Posted by Dr.Montazer

Hi,

Well, as new member in OpenFoam (days of experience in OpenFoam) I would say using dsmcFoam (Direct simulation Monte Carlo (DSMC) solver for 3D, transient, multi- species flows) might help

Back in my Fluent experience, you have to use the Multiphase model and depends to the nature of component (mixture, Eulerian or VOF) will works fine. Looks the same approach is working in OpenFoam:

-compressibleInterFoam: Solver for 2 compressible, isothermal immiscible fluids using a VOF (volume of fluid) phase-fraction based interface capturing approach, )

More could be find at Standard solvers: http://www.openfoam.com/features/standard-solvers.php

I'm not sure this is related to the topic.
Maybe you have mixed up your answers ...

[m.beh]

Originally Posted by gearboy

You can use the following equation
pi=C_P(c,t)*gas_molar_fraction
where, pi is the partial pressure, C_P(c,t) gets the mixed gas pressure.
gas_molar_fraction is the mole fraction of a species in the mixture, which can be calculated by
- first summing up [mass fraction / molecular weight] of all species and
- then dividing the same quotient for the individual species by the calculated sum.
This is done automatically by the following function call (including variables and preparation):
Material *mix_mat = mixture_material(Get_Domain(1));
Material *spe_mat = NULL;
real all_mass_fracts[MAX_SPE_EQNS];
real all_mole_fracts[MAX_SPE_EQNS];
int i = -1;
mixture_species_loop(mix_mat, spe_mat, i)
{
all_mass_fracts[i] = C_YI(c,t,i);
}
Mole_Fraction(mix_mat, all_mass_fracts, all_mole_fracts)
After this, the mole fractions of all species can be found in the array "all_mole_fracts".

Hi every body

I want to have my species' partial pressure but the problem is that I have back flow in my simulating.(I simulate a 2D bubble column). so the static pressure that I recive from (c_P()) is negetive in some cells.
do you think using the absolute of static pressure is ok? my codeis becom:
Po2= abs(C_P(c,t))*mol_fraction_o2

[hossein65]

You can also calculate the molar concentration first:

mol_conc = yi[0] * C_R(c, t) / mw[0];

where:

mol_conc: molar concentration
yi[PHASE_INDEX]: mass fraction of species i in the phase you are working on
C_R(c, t): MACRO for Gas constan
mw_i [0]: Molecular weight of species i

Then, with the ideas gas law you can convert the molar concentration to partial pressure:

PV=nRT ---> P=
=RT

where is the molar concentration calculated above.

[Goenitz]

Originally Posted by hossein65

You can also calculate the molar concentration first:

mol_conc = yi[0] * C_R(c, t) / mw[0];

where:

mol_conc: molar concentration
yi[PHASE_INDEX]: mass fraction of species i in the phase you are working on
C_R(c, t): MACRO for Gas constan
mw_i [0]: Molecular weight of species i

Then, with the ideas gas law you can convert the molar concentration to partial pressure:

PV=nRT ---> P=
=RT

where is the molar concentration calculated above.

How to use partial pressure in rate equation? For example As CFX is saying prefix to 'p' is not recognised
LIBRARY:
CEL:
EXPRESSIONS:
kconst=Arr*((CH4.p)^0.47)*((H2O.p)^0.01)
END
END
END

LIBRARY:
CEL:
EXPRESSIONS:
Arr= 0.390 [mol s^-1 Pa^-0.46]
END
END
END

LIBRARY:
CEL:
EXPRESSIONS:
Eact = 43200 [J mol^-1]
END
END
END


LIBRARY:
CEL:
EXPRESSIONS:
Rate= kconst* e^(-Eact/R/T)
END
END