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-   -   therm.dat NASA polynomials (http://www.cfd-online.com/Forums/openfoam/78989-therm-dat-nasa-polynomials.html)

mystix August 9, 2010 07:15

therm.dat NASA polynomials
 
Hallo Foamers,

according to http://www.me.berkeley.edu/gri_mech/data/nasa_plnm.html there are 7 coefficients that define the material properties (c_p, H, S) for the temperature under 1000 K. When is the therm.dat file used?

Am I right, when I claim, that can only be a rough estimation? The jump discontinuity of material properties at the change from liquid to gas phase is not represented exactly only with these 7 coefficients.

My second question is about the ...src/thermophysicalModels/liquids/C10H22/C10H22.H file.
I think the material properties are calculated with the NSRDS-functions using the parameters in the C10H22.H file. Is this right?

c_p is now calculated two times. First in the therm.dat file and second in the liquids folder. What is used when?

Please bring some light into the dark.

Best regards
Markus

niklas August 9, 2010 07:38

Quote:

Originally Posted by mystix (Post 270808)
according to http://www.me.berkeley.edu/gri_mech/data/nasa_plnm.html there are 7 coefficients that define the material properties (c_p, H, S) for the temperature under 1000 K. When is the therm.dat file used?

when you use multiple species

Quote:

Originally Posted by mystix (Post 270808)
Am I right, when I claim, that can only be a rough estimation? The jump discontinuity of material properties at the change from liquid to gas phase is not represented exactly only with these 7 coefficients.

yes, therm.dat only applies for gaseous properties, but what jump discontinuties are you referring to? The enthalpy of the liquid is calculated (in dieselSpray) using the therm.dat gas-enthalpy and the liquid NSRDS latent heat function to avoid inconsistensies. There are some gas-properties available in the liquids as well, but I dont think they are used anywhere at the moment.
They have only been included because the data is there, so why not include it in case it
might be needed in the future.

Quote:

Originally Posted by mystix (Post 270808)
My second question is about the ...src/thermophysicalModels/liquids/C10H22/C10H22.H file.
I think the material properties are calculated with the NSRDS-functions using the parameters in the C10H22.H file. Is this right?

yes, but only for the liquid properties.

Quote:

Originally Posted by mystix (Post 270808)
c_p is now calculated two times. First in the therm.dat file and second in the liquids folder. What is used when?

c_p for the liquid properties are calculated using the NSRDS-functions, ie the liquids/C10H12.H file,
whereas the c_p for the gas is calculated using the therm.dat file.

mystix August 9, 2010 10:25

Thank you for answer :)

You are right, there is no jump discontinuity when the gas phase and the liquid phase properties are determined in the therm.dat respectively in the liquid-folder.

I am just confused by
Quote:

when you use multiple species
When I have a single component fuel the therm.dat is not used?

How is therm.dat file used when I have a 3 component fuel (35% C6H14, 40% C7H16, 25% C10H22)?

A parcel represents droplets with the same properties like velocity and temperature. When I have a 3 component mixture a parcel represents the well mixed mixture of these 3 components. The concentrations of the species change not spatial in one parcel but over time, due to different material properties. All conservation equations are calculated for every component.
The liquid evaporates and changes to the gas phase. Is now the therm.dat file used or when does the therm.dat takes influence?

niklas August 9, 2010 13:55

Quote:

Originally Posted by mystix (Post 270827)
When I have a single component fuel the therm.dat is not used?

yes it is.You say you have 1 species, but that's just the fuel, what about the other species, like N2, O2 etc.

Quote:

Originally Posted by mystix (Post 270827)
How is therm.dat file used when I have a 3 component fuel (35% C6H14, 40% C7H16, 25% C10H22)?

The same as if you would have only 1 species, or a billion.

Quote:

Originally Posted by mystix (Post 270827)
A parcel represents droplets with the same properties like velocity and temperature. When I have a 3 component mixture a parcel represents the well mixed mixture of these 3 components. The concentrations of the species change not spatial in one parcel but over time, due to different material properties. All conservation equations are calculated for every component.
The liquid evaporates and changes to the gas phase. Is now the therm.dat file used or when does the therm.dat takes influence?

therm.dat is used whenever you related the enthalpy, temperature and specie concentrations in the gas phase.
I can't write it much clearer than that.

mystix August 20, 2010 07:21

Quote:

There are some gas-properties available in the liquids as well, but I dont think they are used anywhere at the moment.
How do you know? The vapour thermal conductivity is only calculated with the NSDRS functions, not in the therm.dat. The vapour diffusivity is only calculated with the API function and not in the therm.dat.

In the therm.dat there are only the gas properties of the thermal conductivity c_p, enthalpy H and entropy S calculated.
This cant be enough :/


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