.FLD file for normal hydrogen and para hydrogen

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Versions

REFPROP Version: REFPROP version 10]
Operating System and Version: Windows 10 64 bits
Access Method: REFPROP standalone

Hi REFPROP users,

I am working with hydrogen (para, ortho and normal) and I would like to be able to reproduce

• the heat of conversion from ortho to para as function of temperature
• the heat of conversion from normal to para as function of temperature

The reference state for ortho hydrogen comes from Le Roy et al, 1990 and the reference states for normal and para are left as NBP to conform with that from earlier versions of Refprop. The .FLD files for para and normal hydrogen describe what should be done to conform with the reference state of ortho hydrogen and to be consistent with the enthalpy and entropy properties of orthohydrogen.

For parahydrogen, the changes suggested for enthalpy value are consistent with the value from Le Roy et al, 1990 and I get the expected value for the enthalpy of conversion from ortho to para.

For normal hydrogen things are tricky because the value for enthalpy is also from Le Roy et al., 1990 but it corresponds to equilibrium hydrogen and not normal hydrogen (so it includes the changes of composition as function of temperature). Could you please confirm that the value that should be use is 1.58275 kJ/mol (75% of ortho and 25% of para).

In addition, I am not able to figure out from where the value considered for entropy are coming. The values are different from ones reported by Le Roy et al., 1990. Could you please provide some explanations ?

Thank you for you help.