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CalebBell / thermo

Thermodynamics and Phase Equilibrium component of Chemical Engineering Design Library (ChEDL)
MIT License
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Strange Cp values for Helium #17

Closed recornell closed 5 years ago

recornell commented 5 years ago

When trying to calculate Cp for helium near STP, I'm getting 1.5931 J/(Kg), which conflicts with several tabulated values of about 5.193 J/(Kg). Here's the code I'm using:

N2 = therm.Chemical('n2',T=293.15)
He = therm.Chemical('helium',T=293.15)
Ar = therm.Chemical('argon',T=293.15)
Cp = np.array([N2.Cpg/1000,He.Cpg/1000,Ar.Cpg/1000])

CalebBell commented 5 years ago

Hi recornell, It seems to happen that none of the various tabulations of heat capacity coefficients in thermo have data for helium. The value you saw came from the next best place - an estimation method for organic compounds. Obviously it did poorly for Helium :)

I have never noticed before because properties from chemicals which are well defined like helium should come from the CoolProp backend of thermo. It is strictly an optional dependency, but you will see once it is installed your problem goes away; and the values from CoolProp should be even more accurate than your tabulation!

Sincerely, Caleb