# How to get partial pressure of oxygen?

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 March 2, 2010, 07:49 How to get partial pressure of oxygen? #1 Senior Member     Sebastian Gatzka Join Date: Mar 2009 Location: Frankfurt, Germany Posts: 729 Rep Power: 20 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. __________________ Schrödingers wife: "What did you do to the cat? It's half dead!"

 March 2, 2010, 17:52 #2 New Member   Jan Join Date: Nov 2009 Posts: 21 Rep Power: 16 i too need the same!

March 3, 2010, 01:51
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Quote:
 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".

 March 4, 2010, 10:31 #4 Senior Member     Sebastian Gatzka Join Date: Mar 2009 Location: Frankfurt, Germany Posts: 729 Rep Power: 20 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? __________________ Schrödingers wife: "What did you do to the cat? It's half dead!"

March 4, 2010, 10:59
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Quote:
 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.

March 4, 2010, 11:07
#6
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Sebastian Gatzka
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Quote:
 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?
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 March 4, 2010, 11:29 #7 Senior Member     Sebastian Gatzka Join Date: Mar 2009 Location: Frankfurt, Germany Posts: 729 Rep Power: 20 Ok. I put this so far into my code 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? __________________ Schrödingers wife: "What did you do to the cat? It's half dead!"

 March 7, 2010, 04:55 How to get partial pressure of oxygen? #8 New Member   Jamshid Montazer Join Date: Mar 2010 Location: Norway Posts: 1 Rep Power: 0 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 __________________ Dr.Montazer Norway

March 7, 2010, 05:02
#9
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Sebastian Gatzka
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Quote:
 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.
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August 8, 2011, 04:12
#10
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Quote:
 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

 April 10, 2017, 10:21 #11 Member   Hossein Join Date: Oct 2010 Location: Greensboro, NC, USA Posts: 30 Rep Power: 15 You can also calculate the molar concentration first: Code: 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. Gomaa and souza.emer like this. __________________ Hossein Amini PhD student in Biochemical Engineering; Computational Science and Engineering department; North Carolina Agricultural and Technical State University

June 13, 2019, 07:04
#12
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Abdullah Arslan
Join Date: Apr 2019
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Quote:
 Originally Posted by hossein65 You can also calculate the molar concentration first: Code: 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

 Tags oxygen, partial pressure