[Mehdi3031]

Hello everybody,
in many cases of openFoam, you can find equation Of State that is modeled as a perfect Fluid such as in:
tutorials/multiphase/compressibleMultiphaseInterFoam/laminar/damBreak4phase/constant/thermophysicalProperties.mercury

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectFluid;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        nMoles      1;
        molWeight   200.59;
    }
    equationOfState
    {
        R           6818;
        rho0        13529;
    }
    thermodynamics
    {
        Cp          139;
        Hf          0;
    }
    transport
    {
        mu          1.522e-3;
        Pr          0.022;
    }
}

or in:
tutorials/multiphase/reactingTwoPhaseEulerFoam/laminar/bubbleColumn/constant/thermophysicalProperties.water

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectFluid;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        nMoles      1;
        molWeight   18;
    }
    equationOfState
    {
        R           3000;
        rho0        1027;
    }
    thermodynamics
    {
        Cp          4195;
        Hf          0;
    }
    transport
    {
        mu          3.645e-4;
        Pr          2.289;
    }
}

There are two parameters "R" and "rho0" that are defined and necessary for perfect liquid model which is defined in OF documentation as following:

I can't figure out what is this value of R which is 3000 for water and 6818 for mercury and how to calculate it for ammonia for example. any Idea?

[meshman]

There is no documentation related above question...

[jiejie]

Originally Posted by Mehdi3031

Hello everybody,
in many cases of openFoam, you can find equation Of State that is modeled as a perfect Fluid such as in:
tutorials/multiphase/compressibleMultiphaseInterFoam/laminar/damBreak4phase/constant/thermophysicalProperties.mercury

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectFluid;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        nMoles      1;
        molWeight   200.59;
    }
    equationOfState
    {
        R           6818;
        rho0        13529;
    }
    thermodynamics
    {
        Cp          139;
        Hf          0;
    }
    transport
    {
        mu          1.522e-3;
        Pr          0.022;
    }
}

or in:
tutorials/multiphase/reactingTwoPhaseEulerFoam/laminar/bubbleColumn/constant/thermophysicalProperties.water

thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       const;
    thermo          hConst;
    equationOfState perfectFluid;
    specie          specie;
    energy          sensibleInternalEnergy;
}

mixture
{
    specie
    {
        nMoles      1;
        molWeight   18;
    }
    equationOfState
    {
        R           3000;
        rho0        1027;
    }
    thermodynamics
    {
        Cp          4195;
        Hf          0;
    }
    transport
    {
        mu          3.645e-4;
        Pr          2.289;
    }
}

There are two parameters "R" and "rho0" that are defined and necessary for perfect liquid model which is defined in OF documentation as following:

I can't figure out what is this value of R which is 3000 for water and 6818 for mercury and how to calculate it for ammonia for example. any Idea?

Hi Mehdi

I am having the same problem. I could not figure out the R of 3000 for water in the twoPhaseEulerFoam tutorial. In particular with respect to rhom (after you run the case) RAS/bubbleCoumn, rhom is around 1027 in the region where alpha.air=0 (meaning water) but rhom is around 513 in the region where alpha.air=1 (meaning air). Shouldn't the rhom be around 1.225 (density of air) in the region where alpha=1?

Thanks
Jie

[tankerp]

Im also having a difficulty in understanding this. What is rhom and why is it as much as 513 in the region representing air?

[anh065]

with being the molecular weight of gas/fluid.

For air, and .


https://en.wikipedia.org/wiki/Ideal_gas_law

[meshman]

According to your solution,

For example, in case of water (H2O)

the molar mass is about 0.018 kg/mol

so the R = 8.314/0.018 ~ 461.9 J/kg K.

This value is not same with '3000' in the above tutorial.

(Actually, I still don't know why the value is 3000....)

[arsimons]

I believe that in OpenFOAM 1806, R = 7255 for water. However, I have no idea what it means...

[jherb]

Have you solved this?



I think if you use R for a liquid, it is just some kind of compressibility of it.



Regarding rhom: It is calculated here:
https://github.com/OpenFOAM/OpenFOAM...Epsilon.C#L403


and it involves the use of a virtual mass model. What are the corresponding settings in your case?

[wildemam]

Originally Posted by arsimons

I believe that in OpenFOAM 1806, R = 7255 for water. However, I have no idea what it means...

If anyone is still wondering:


R is (RT)^(-1)


For water, it should be calculated from psi, the compressiblity.


psi = rho/bulk modulus, giving around 4.5e-7 s2/m2
(check here https://www.openfoam.com/documentati...x12-620003.3.1)


then R = 7255.

the use of 3000 is a mystery.

[krasus]

Originally Posted by wildemam

If anyone is still wondering:


R is (RT)^(-1)


For water, it should be calculated from psi, the compressiblity.


psi = rho/bulk modulus, giving around 4.5e-7 s2/m2
(check here https://www.openfoam.com/documentati...x12-620003.3.1)


then R = 7255.

the use of 3000 is a mystery.

Thanks for the clue. However, can you show how to calculate R from psi? I can't figure out how (RT)^-1 and psi is correlated.

[Tobermory]

psi is defined as drho/dp|_T, and so for an ideal gas psi = rho/p = 1/RT. This is referred to as the compressibility. R is the ideal gas constant over the molecular weight; it doesn't have any meaning for a liquid.

[krasus]

Originally Posted by Tobermory

psi is defined as drho/dp|_T, and so for an ideal gas psi = rho/p = 1/RT. This is referred to as the compressibility. R is the ideal gas constant over the molecular weight; it doesn't have any meaning for a liquid.

Thanks for the info!