Temperature dependent Specific Heat Capacity in multiphaseEulerFoam

SAIKRISHNA N · October 27, 2022, 03:00

Hello All,
I am using reactingTwoPhaseEulerFoam/multiphaseEulerFoam solvers. I am trying to implement Cp(T) using hPolynomial. Since, 2 phases are involved, I am specifying Cp(T) for liquid and gas separately. I found that enthalpy calculated by OpenFOAM7 for liquid phase and vapor phase, both are OFF to actual values. I observed the source code and found that it uses
h = integral(Cp(T)) from Tstd to T + Hf
Here, I am giving Hf = 0 as input for both phases.
I am not getting Tstd value anywhere in source code.

Due to this latent heat estimation is also going wrong.

Please let me know,
1. what is the value of Tstd?
2. How to calculate and specify Hf so that I would get correct enthalpy values?

Thank you.

überschwupper · October 27, 2022, 03:32

Hello,

Tstd is Standard temperature, as well as Pstd is standard pressure (298.15K, 1e+5)

defined in /etc/controlDict

you can choose: either you look for the formation enthalpy at reference temperature and pressure in tabulated data

or you calculate the formation enthalpy by balancing each atomic/molecular contribution to the product itself.

Some values can be found here: (for example)

https://atct.anl.gov/Thermochemical%....124/index.php
or VDI Wärmeatlas /Heat atlas

How to balance (hgavent checked it intensively, but looks correct, just first result from google

)

https://chem.libretexts.org/Courses/...y_of_Formation

Take care of the units! OF needs SI units, those values are often given in kJ/mol.
And as addition: Don't be confused, some molecules are by default defined as 0

SAIKRISHNA N · October 27, 2022, 04:09

Hi,

Thanks for the Tstd and Pstd value reference location.

Actually, my intention is to get correct enthalpy values for liquid and vapor. When I simply do a curve fit to Cp(T) data from NIST and give as input hPolynomial, the enthalpy calculated by OpenFOAM is coming offset from actual values. I tried to give the offset values as Hf, since the offset is constant throughout the temperature range. But, i found from source code that
sensibleEnthalpy doesn't consider Hf.

I tried to use absoluteEnthalpy in energy type. But, it has thrown error, 'unknown rhoThermo type'.
what to do?

I am using
type heRhoThermo
mixture pureMixture
transport polynomial
thermo hPolynomial
equationOfState icoPolynomial
specie specie
energy sensibleEnthalpy

when I did, energy type as absoluteEnthalpy above then error came 'unknown rhoThermo type'

October 27, 2022, 03:00	Temperature dependent Specific Heat Capacity in multiphaseEulerFoam	#1
SAIKRISHNA N New Member SAIKRISHNA N Join Date: Jun 2014 Posts: 10 Rep Power: 12	Hello All, I am using reactingTwoPhaseEulerFoam/multiphaseEulerFoam solvers. I am trying to implement Cp(T) using hPolynomial. Since, 2 phases are involved, I am specifying Cp(T) for liquid and gas separately. I found that enthalpy calculated by OpenFOAM7 for liquid phase and vapor phase, both are OFF to actual values. I observed the source code and found that it uses h = integral(Cp(T)) from Tstd to T + Hf Here, I am giving Hf = 0 as input for both phases. I am not getting Tstd value anywhere in source code. Due to this latent heat estimation is also going wrong. Please let me know, 1. what is the value of Tstd? 2. How to calculate and specify Hf so that I would get correct enthalpy values? Thank you.

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October 27, 2022, 03:32		#2
überschwupper Member Join Date: Jan 2022 Location: Germany Posts: 72 Rep Power: 4	Hello, Tstd is Standard temperature, as well as Pstd is standard pressure (298.15K, 1e+5) defined in /etc/controlDict you can choose: either you look for the formation enthalpy at reference temperature and pressure in tabulated data or you calculate the formation enthalpy by balancing each atomic/molecular contribution to the product itself. Some values can be found here: (for example) https://atct.anl.gov/Thermochemical%....124/index.php or VDI Wärmeatlas /Heat atlas How to balance (hgavent checked it intensively, but looks correct, just first result from google ) https://chem.libretexts.org/Courses/...y_of_Formation Take care of the units! OF needs SI units, those values are often given in kJ/mol. And as addition: Don't be confused, some molecules are by default defined as 0

October 27, 2022, 04:09		#3
SAIKRISHNA N New Member SAIKRISHNA N Join Date: Jun 2014 Posts: 10 Rep Power: 12	Hi, Thanks for the Tstd and Pstd value reference location. Actually, my intention is to get correct enthalpy values for liquid and vapor. When I simply do a curve fit to Cp(T) data from NIST and give as input hPolynomial, the enthalpy calculated by OpenFOAM is coming offset from actual values. I tried to give the offset values as Hf, since the offset is constant throughout the temperature range. But, i found from source code that sensibleEnthalpy doesn't consider Hf. I tried to use absoluteEnthalpy in energy type. But, it has thrown error, 'unknown rhoThermo type'. what to do? I am using type heRhoThermo mixture pureMixture transport polynomial thermo hPolynomial equationOfState icoPolynomial specie specie energy sensibleEnthalpy when I did, energy type as absoluteEnthalpy above then error came 'unknown rhoThermo type'