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Enthalpy to temperature

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Old   November 1, 2010, 06:25
Default Enthalpy to temperature
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Adhiraj
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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.
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Old   July 17, 2011, 04:39
Default h to T conversion
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Hi,

I have exactly the same question.

Thanks

Farshad
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Old   July 17, 2011, 10:37
Default Enthalpy to T
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Adhiraj
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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.
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Old   February 13, 2012, 11:51
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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?
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Old   February 13, 2012, 18:35
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Check under
Quote:
$FOAM_SRC/thermophysicalModels/specie/thermo/specieThermo
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Old   February 14, 2012, 04:44
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isabel
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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?
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Old   February 14, 2012, 10:25
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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.
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Old   February 14, 2012, 10:43
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It is a C++ keyword. "this" acts like a pointer to the object whose member function is under consideration.
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Old   February 15, 2012, 10:15
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isabel
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Dear friends,

I have another doubt about these files. Where are defined the functions F and dFdT?
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Old   February 15, 2012, 10:25
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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.
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Old   February 16, 2012, 05:32
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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:




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?

Last edited by isabel; February 16, 2012 at 06:11.
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Old   March 21, 2012, 19:58
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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.
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Old   July 20, 2012, 22:00
Question A Little question?
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Luis Felipe Gutierrez Marcantoni
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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.
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Last edited by lfgmarc; July 21, 2012 at 09:14.
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Old   June 13, 2014, 11:07
Default Enthalpy-temperature for melting problem
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Mohammad Shakil Ahmmed
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Hi isabel ,
Will you please guide me how you implemented the melting problem ?
thanks in advance.

Quote:
Originally Posted by isabel View Post
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:




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?
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