CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   OpenFOAM Programming & Development (http://www.cfd-online.com/Forums/openfoam-programming-development/)
-   -   Enthalpy to temperature (http://www.cfd-online.com/Forums/openfoam-programming-development/81597-enthalpy-temperature.html)

adhiraj November 1, 2010 06:25

Enthalpy to temperature
 
Hi all,
I am new to OpenFOAM. I was looking at where OpenFOAM does the h to T (or hs top T) conversion, and I noted that they use a Newton iteration mthod. But when I try to trace the sepcific heat they use in this equation, they seem to use Cp=Cp(T) and not Cp=Cp(T,Yi). This is the file I am talking about:-
$FOAM/src/thermophysicalModels/specie/thermo/janaf
Can anyone confirm/explain this?
Thanks in advance.

Farshad_Noravesh July 17, 2011 04:39

h to T conversion
 
Hi,

I have exactly the same question.

Thanks

Farshad

adhiraj July 17, 2011 10:37

Enthalpy to T
 
I have dug deep since this post, and have the answers. When they go for the h->T conversion they hold the composition fixed, and define a new 'gas' with the composition averaged thermal properties. It is the Cp of this mixture gas that is (rightly) used to compute T.

isabel February 13, 2012 11:51

Hi all,

I am looking for the extract of the code where the conversion from h to T is done but I do not find it. Can anybody tell me where it is?

adhiraj February 13, 2012 18:35

Check under
Quote:

$FOAM_SRC/thermophysicalModels/specie/thermo/specieThermo

isabel February 14, 2012 04:44

Thank you very much. I found the iteration in these lines:


// return the temperature corresponding to the value of the
// thermodynamic property f, given the function f = F(T) and dF(T)/dT
template<class thermo>
inline scalar specieThermo<thermo>::T
(
scalar f,
scalar T0,
scalar (specieThermo<thermo>::*F)(const scalar) const,
scalar (specieThermo<thermo>::*dFdT)(const scalar) const
) const
{
scalar Test = T0;
scalar Tnew = T0;
scalar Ttol = T0*tol_;
int iter = 0;

do
{
Test = Tnew;
Tnew = Test - ((this->*F)(Test) - f)/(this->*dFdT)(Test);

if (iter++ > maxIter_)
{
FatalErrorIn
(
"specieThermo<thermo>::T(scalar f, scalar T0, "
"scalar (specieThermo<thermo>::*F)(const scalar) const, "
"scalar (specieThermo<thermo>::*dFdT)(const scalar) const"
") const"
) << "Maximum number of iterations exceeded"
<< abort(FatalError);
}

} while (mag(Tnew - Test) > Ttol);

return Tnew;
}


There is something I do not understhand. What does “this->” means?

megacrout February 14, 2012 10:25

I might be wrong but I donīt think this is an OF-specific function.
Ecosia (instead of googling it) "this pointer" or "this pointer c++" or such.
Tibo

adhiraj February 14, 2012 10:43

It is a C++ keyword. "this" acts like a pointer to the object whose member function is under consideration.

isabel February 15, 2012 10:15

Dear friends,

I have another doubt about these files. Where are defined the functions F and dFdT?

adhiraj February 15, 2012 10:25

They are the function and its derivative.
The Newton iteration in this case calculates T, given F(T) and dF/dT(T).
The function gets pointers to the functions F and dF/dt.

If the energy variable is enthalpy h, then F=h(T) and dF/dt=Cp(T).
If it is internal energy e, then F=e and dF/dT=Cv(T).

The code resolves these at runtime, and sends the appropriate pointers to the Newton iteration routine.

isabel February 16, 2012 05:32

Dear friends,

Thank you very much for your help. I need to simulate melting of a solid. In that case, the enthalpy is given by the following equation:

http://fotos.miarroba.es/lamasgaldo/4-energy-equation3/ http://fotos.miarroba.es/lamasgaldo/4-energy-equation3/ http://fotos.miarroba.es/lamasgaldo/...3/#anchorPhotohttp://www.cfd-online.com/Forums/[im...3/#anchorPhotohttp://fotos.miarroba.es/lamasgaldo/...3/#anchorPhoto http://fotos.miarroba.es/lamasgaldo/...-equation3.jpg http://fotos.miarroba.es/lamasgaldo/3-energy-equation3
http://fotos.miarroba.es/th/32d6/204...2D4F3CD61F.jpg

where L is the latent heat and alpha_l the mass fraction of the liquid phase.

How do I implement the term alpha_l*L in the functions F and dFdT?

adhiraj March 21, 2012 19:58

Hi,
I would use
Code:

    F=H
    dFdT=Cp

This is because, H=H(T) is the relationship you are trying to invert.
And, at that point you will typically hold the composition fixed, so that \alpha, L and H_{ref} are fixed. So, dFdT=Cp.
This of course assumes that L is not a function of T.

lfgmarc July 20, 2012 22:00

A Little question?
 
Hi, I have a little question,

I understand that if i.e, the energy variable is enthalpy F=h(T) and dF/dT=Cp(T), my question is in where it is defined in the code that F and dF/dt take these variables as arguments.

Thanks in advance.

ahmmedshakil June 13, 2014 11:07

Enthalpy-temperature for melting problem
 
Hi isabel ,
Will you please guide me how you implemented the melting problem ?
thanks in advance.

Quote:

Originally Posted by isabel (Post 344726)
Dear friends,

Thank you very much for your help. I need to simulate melting of a solid. In that case, the enthalpy is given by the following equation:

http://fotos.miarroba.es/lamasgaldo/4-energy-equation3/ http://fotos.miarroba.es/lamasgaldo/4-energy-equation3/ http://fotos.miarroba.es/lamasgaldo/...3/#anchorPhotohttp://www.cfd-online.com/Forums/[im...3/#anchorPhotohttp://fotos.miarroba.es/lamasgaldo/...3/#anchorPhoto http://fotos.miarroba.es/lamasgaldo/...-equation3.jpg http://fotos.miarroba.es/lamasgaldo/3-energy-equation3
http://fotos.miarroba.es/th/32d6/204...2D4F3CD61F.jpg

where L is the latent heat and alpha_l the mass fraction of the liquid phase.

How do I implement the term alpha_l*L in the functions F and dFdT?



All times are GMT -4. The time now is 04:21.