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-   -   Thermodynamics database (http://www.cfd-online.com/Forums/openfoam-solving/60408-thermodynamics-database.html)

grtabor July 25, 2005 11:11

Hi. I'm puzzling out the therm
 
Hi. I'm puzzling out the thermodynamics modelling in FOAM... I'm looking at the thermophysicalProperties dictionary in the moriyoshiHomogeneous test case in the tutorials. There are entries for each different component of the combustion process (I can understand this) - fuel, oxidant, reactants, products, and burntProducts. 4 entries I can understand; but what is the difference between products and burntProducts? Thanks.

Gavin

lucchini July 25, 2005 11:27

Hi Gavin. It depends on the
 
Hi Gavin.

It depends on the mixture you choose in the mixtureType template.

homogeneousMixture:it is for a mixture with a constant air to fuel ratio in all the mesh. In this case you should have to specify only the thermodynamic properties of the "reactants" (air and fuel) and "products" (burnt gases). The cell thermodynamic properties will depend only by the burnt mass fraction b.

inhomogeneousMixture: it is used for a mixture with variable air to fuel ratio, so also the chemical composition of products and reactants will be different cell by cell, depending on the air/fuel ratio ("ft"). In fact where the mixture is lean the mixture is composed by "products", and "oxidant", while the mixture is rich the composition is given by "fuel" and "products". So the thermodynamic properties will depend not only by b, but also by the fuel fraction ft.

To understand it better you should give a look in the $FOAM_SRC/thermophysicalModels/combustion/mixtureThermo/mixtures

grtabor July 25, 2005 11:38

Hi Tommaso, Thanks for the
 
Hi Tommaso,

Thanks for the clear description of homogeneous vs inhomogeneous - I think I probably want homogeneous (based on simplicity and the rest of my modelling). However I still don't understand the difference between 'products' and 'burntProducts'. Is it that one is used for homogeneousMixture and one for inhomogeneousMixture?

No .. delete that last: I've looked at the source files and that is indeed what is happening. Thanks again.

Gavin

grtabor July 26, 2005 10:47

One further question; in the U
 
One further question; in the Users Guide it states that the hConstThermo database needs the heat of fusion of the species as its second entry. Why? I'm trying to set up for methane combustion; nothing is ever likely to turn into a liquid even, let alone freeze solid??

Gavin

liugx212 November 29, 2005 18:06

Hi Tommaso and Gavin: As yo
 
Hi Tommaso and Gavin:

As you said, The different properties (mechanical properties) for different cells can ne set if we want, right? But my question is how to set them? I really need the help from you.

Thanks deeply.

Guoxaing

liugx212 November 29, 2005 18:07

Hi Tommaso and Gavin: As yo
 
Hi Tommaso and Gavin:

As you said, The different properties (mechanical properties) for different cells can be set if we want, right? But my question is how to set them? I really need the help from you.

Thanks deeply.

Guoxaing


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