[johanz]

I am using OpenFOAM 2.2.0.

I am busy using the chtMultiRegionFoam solver to configure a heat transfer case that involves multiple materials. When I started editing the thermophysicalProperties files, I found it very hard to determine what the units of the properties were. I am referring to the following content of the file:

mixture
{
specie
{
nMoles 1;
molWeight 63.546; // molar weight, [kg/kmol]
}

transport
{
kappa 401; // thermal conductivity, [W/(m.K)]
}

thermodynamics
{
Hf 0; // ??? enthalpy of formation, [J/kmol]
Cp 24449; // heat capacity at constant pressure, [J/(kmol K)], ref. FactSage FactPS database
}

equationOfState
{
rho 8960; // density, [kg/m^3]
}
}

I delved into the header files to find comments where the units were documented. These parameters are implemented with the scalar data type, and not a dimensionedScalar data type. This makes me a bit worried.

Is there a specific method in that I can use to determine the units of quantities such as those above, or are the units implicitly implemented in the code with comments documenting the choice of units?

Was the implementation of units on thermophysical properties changed in version 2.2.0 to eliminate the units? If so, what is the reason for this.

Thanks for the help.

Johan

[jherb]

Originally Posted by johanz

I am using OpenFOAM 2.2.0.
...

mixture
{
    ...
thermodynamics
    {
        Hf      0; // ??? enthalpy of formation, [J/kmol]
        Cp      24449; // heat capacity at constant pressure, [J/(kmol K)], ref. FactSage FactPS database
    }
...

...

Comparing the example given at http://www.openfoam.org/docs/user/thermophysical.php with the value (for air) from https://en.wikipedia.org/wiki/Heat_capacity it looks like cp is in J/(kg K) and not J/(kmol K).

In the bug report http://www.openfoam.org/mantisbt/view.php?id=1008#c2487 it is explained that:

In the source code, typically upper case letters (e.g. Ha) indicate [J/kg] and lower case (e.g. ha) [J/kmol].

Internally in https://github.com/OpenFOAM/OpenFOAM...ThermoI.H#L129 the sensible enthalpy is calculated which has the units J/kmol (according to https://github.com/OpenFOAM/OpenFOAM...tThermo.H#L154) so cp has the units J/(kmol K). The conversion is from kg to kmol is done when reading it in https://github.com/OpenFOAM/OpenFOAM...stThermo.C#L52

The same seems to apply to Hf (so also given as J/kg in thermophysicalProperties)

[deepbandivadekar]

Originally Posted by jherb

Comparing the example given at http://www.openfoam.org/docs/user/thermophysical.php with the value (for air) from https://en.wikipedia.org/wiki/Heat_capacity it looks like cp is in J/(kg K) and not J/(kmol K).

In the bug report http://www.openfoam.org/mantisbt/view.php?id=1008#c2487 it is explained that:
Internally in https://github.com/OpenFOAM/OpenFOAM...ThermoI.H#L129 the sensible enthalpy is calculated which has the units J/kmol (according to https://github.com/OpenFOAM/OpenFOAM...tThermo.H#L154) so cp has the units J/(kmol K). The conversion is from kg to kmol is done when reading it in https://github.com/OpenFOAM/OpenFOAM...stThermo.C#L52

The same seems to apply to Hf (so also given as J/kg in thermophysicalProperties)

Sorry for bumping this again. But I'm confused a bit about this explanation.
If, according to this, Hf is in J/kg, for water the value should be approximately 3.33e5 (J/kg). Following is an excerpt from the thermophysicalProperties directory of bubbleColumnEvaporator tutorial.

    thermodynamics
    {
        Hf          -1.5879e+07;
        Cp          4195;
    }

How do we explain this? Not just a question of units but of the actual magnitude as well.
(A quick way to compare different ways in which Hf is defined in all tutorials:

find <tutorial path> -name thermoPhysicalProperties | xargs grep -rn "Hf "

This is what I did to check how it was defined in various scenarios.)