Cv/Cp in Openfoam 8?

Clau.77 · August 18, 2021, 08:00

Hey guys!

So i measured some Cp values, got a polynomial function and now want to use it for my solid region in my multiregion case.

I noticed, that in OF8 the input value is Cv and not Cp. Do i need to calculate the cv values first? (I mean cv = cp-R). Or is OF allready doing that by itself since I the molar Mass is also given in the thermodynamicProperties file?

Please don't tell me to look into the code, i tried that but sinde i am not familiar with C++ (or programming in general) it is super confusing for me.

I'd appreciate some help here

Yann · August 18, 2021, 10:17

Hi Claudia,

This is related to the fact the energy form for solids has been switched from sensibleEnthalpy to sensibleInternalEnergy in OpenFOAM 8 : https://github.com/OpenFOAM/OpenFOAM...d30ec6916e73a1

Since the cases use sensibleInternalEnergy now, Cv is used instead of Cp. (see documentation here)

You can either switch you solid back to sensibleEnthalpy or keep it this way and use Cv values.

Since solids are usually considered incompressible, I am not sure there is a significant difference between Cp and Cv.

I hope this helps,
Yann

August 18, 2021, 08:00	Cv/Cp in Openfoam 8?	#1
Clau.77 Member Claudia Join Date: Mar 2021 Posts: 43 Rep Power: 5	Hey guys! So i measured some Cp values, got a polynomial function and now want to use it for my solid region in my multiregion case. I noticed, that in OF8 the input value is Cv and not Cp. Do i need to calculate the cv values first? (I mean cv = cp-R). Or is OF allready doing that by itself since I the molar Mass is also given in the thermodynamicProperties file? Please don't tell me to look into the code, i tried that but sinde i am not familiar with C++ (or programming in general) it is super confusing for me. I'd appreciate some help here

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August 18, 2021, 10:17		#2
Yann Senior Member Yann Join Date: Apr 2012 Location: France Posts: 1,071 Rep Power: 26	Hi Claudia, This is related to the fact the energy form for solids has been switched from sensibleEnthalpy to sensibleInternalEnergy in OpenFOAM 8 : https://github.com/OpenFOAM/OpenFOAM...d30ec6916e73a1 Since the cases use sensibleInternalEnergy now, Cv is used instead of Cp. (see documentation here) You can either switch you solid back to sensibleEnthalpy or keep it this way and use Cv values. Since solids are usually considered incompressible, I am not sure there is a significant difference between Cp and Cv. I hope this helps, Yann