How are the integration constants for the JANAFthermo class derived?

tomf · March 9, 2011, 03:27

Dear all,

I am looking for a bit more information on the derivation of the integration constants for the JANAFthermo. As explained in the user guide:http://www.openfoam.com/docs/user/th...hp#x37-2040012 we have 2 times 7 constants that are required for the thermodynamic properties. One set for a low temperature regime, and one set for the high temperature regime. For these sets, the first 5 constants create the polynomial function to calculate Cp as a function of T. Than there are two integration constants, which are mentioned in the User Guide. One is used to determine the enthalpy and one for the entropy. However it is not quite clear to me how these constants are derived. What is the integration that is performed which leads to these integration constant? So how to determine these constants from thermodynamic data?

I hope someone can explain this.

Kind regards,

Tom

ziemowitzima · May 14, 2015, 05:51

Hi,
I was long time ago, but I have similar question.
Did you manage to find the aswer ?

I general we have Cp(T), then:
1. H = integral(CP) dT + constant1
2. S = integral(CP/T)dT + constant2

but what is the value of the constant1 and constant2 ?

best

tomf · May 15, 2015, 07:47

Hi,

Unfortunately I do not remember exactly. I believe I ultimately found the data I needed somewhere. For the enthalpy I think it is based on the formation enthalpy, but I do not think I needed the entropy part.

So basically I do not think I can help you any further.

Regards,
Tom

March 9, 2011, 03:27	How are the integration constants for the JANAFthermo class derived?	#1
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 634 Rep Power: 32	Dear all, I am looking for a bit more information on the derivation of the integration constants for the JANAFthermo. As explained in the user guide:http://www.openfoam.com/docs/user/th...hp#x37-2040012 we have 2 times 7 constants that are required for the thermodynamic properties. One set for a low temperature regime, and one set for the high temperature regime. For these sets, the first 5 constants create the polynomial function to calculate Cp as a function of T. Than there are two integration constants, which are mentioned in the User Guide. One is used to determine the enthalpy and one for the entropy. However it is not quite clear to me how these constants are derived. What is the integration that is performed which leads to these integration constant? So how to determine these constants from thermodynamic data? I hope someone can explain this. Kind regards, Tom

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May 14, 2015, 05:51		#2
ziemowitzima Senior Member Mieszko Młody Join Date: Mar 2009 Location: POLAND, USA Posts: 145 Rep Power: 17	Hi, I was long time ago, but I have similar question. Did you manage to find the aswer ? I general we have Cp(T), then: 1. H = integral(CP) dT + constant1 2. S = integral(CP/T)dT + constant2 but what is the value of the constant1 and constant2 ? best

May 15, 2015, 07:47		#3
tomf Senior Member Tom Fahner Join Date: Mar 2009 Location: Breda, Netherlands Posts: 634 Rep Power: 32	Hi, Unfortunately I do not remember exactly. I believe I ultimately found the data I needed somewhere. For the enthalpy I think it is based on the formation enthalpy, but I do not think I needed the entropy part. So basically I do not think I can help you any further. Regards, Tom