Newer Janaf Model

immortality · February 7, 2016, 10:22

Quote:

Originally Posted by ziemowitzima

It seems that this question was not answered (but asked several times in the upper discussion).

Is anyone of you aware how the constants of integration are calculated ?

I know that:

$H(T) = \int Cp(T) \, dT + C1$

$S(T) = \int \frac{Cp(T)}{T} \, dT + C2$

but what is the value of C1 and C2, which is needed for JANAF as a6 and a7 ?

thanks
ZMM

hi
there are tables for JANAF values for various materials in net or in thermodynamics books like van wylen,... I remember I found them although wasn't easy enough.

adrieno · April 7, 2016, 10:32

Hi Punit Walia,
I'm in the same case as yours, did you get any answer ?
Thank you
Adrien

DustExplosion · October 13, 2016, 06:59

This is an old thread, but the link for the old janaf tables is down. I was wondering if anyone could post a new link or the old files?

I will use the new ones for now, but they are overkill for my problem.

saturn_K · October 28, 2020, 06:26

Dear Foamers

In OFv7 and OFv2006 and other earlier versions, in janafThermoI.H file, calculation of dGdT (Gibbs free energy derivative w.r.t. temperature) is expressed as:

Code:

 template<class EquationOfState>
 inline Foam::scalar Foam::janafThermo<EquationOfState>::dGdT
 (
     const scalar p,
     const scalar T
 ) const
 {
     const coeffArray& a = coeffs(T);
     return -((a[0] + a[5]/T)/T + a[1]/2 + T*(a[2]/3 + T*(a[3]/4 + T*a[4]/5)));
 }

As far as I know, dGdT is equal to -S but as you can see in the above expression, dGdT is calculated based on the H expression coefficients (i.e it has a[5]). In fact, according to these, we can say dGdT is equal to -H°(T)/RT^2.
It may be a silly question, but could anybody please explain why is this so?

Thank you

October 28, 2020, 06:26	Gibbs free energy derivative expression w.r.t. temperature	#44
saturn_K New Member Join Date: Sep 2019 Posts: 14 Rep Power: 6	Dear Foamers In OFv7 and OFv2006 and other earlier versions, in janafThermoI.H file, calculation of dGdT (Gibbs free energy derivative w.r.t. temperature) is expressed as: Code: template<class EquationOfState> inline Foam::scalar Foam::janafThermo<EquationOfState>::dGdT ( const scalar p, const scalar T ) const { const coeffArray& a = coeffs(T); return -((a[0] + a[5]/T)/T + a[1]/2 + T(a[2]/3 + T(a[3]/4 + T*a[4]/5))); } As far as I know, dGdT is equal to -S but as you can see in the above expression, dGdT is calculated based on the H expression coefficients (i.e it has a[5]). In fact, according to these, we can say dGdT is equal to -H°(T)/RT^2. It may be a silly question, but could anybody please explain why is this so? Thank you febriyan91 likes this.

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April 7, 2016, 10:32		#42
adrieno Member AdOo Join Date: Mar 2016 Location: Bordeaux Posts: 91 Rep Power: 9	Hi Punit Walia, I'm in the same case as yours, did you get any answer ? Thank you Adrien

October 13, 2016, 06:59		#43
DustExplosion Member Chris Cloney Join Date: Jun 2016 Location: Halifax, Canada Posts: 62 Rep Power: 9	This is an old thread, but the link for the old janaf tables is down. I was wondering if anyone could post a new link or the old files? I will use the new ones for now, but they are overkill for my problem.