The thermophysical property results of the two-phase region for a CO₂–O₂ mixture differ between DLL function calls and software interface calls.

[BboyArrow1]

The mass fractions of carbon dioxide and oxygen are 0.89243 and 0.10757, respectively.The pressure and entropy are 9.5 MPa and 260.49 kJ/kg, respectively.The figure below shows the query results from the software interface.

However, when using the DLL interface for the call, the results are shown in the figure below.

It can be seen that many thermophysical property results are incorrect; however, when the state point is far from the bubble point, that is, when the quality increases, the results obtained by the two calling methods become consistent.The figure below shows the function call for 𝑇(𝑝,ℎ). How can I avoid the inconsistency between the results obtained from the DLL call and those from the software interface?

[BboyArrow1]

[Matthew-Boyd]

I think the best method is to call REFPROPdll. Using the Python interface:

from ctREFPROP.ctREFPROP import REFPROPFunctionLibrary
import os

RP = REFPROPFunctionLibrary(os.environ['RPPREFIX'])
RP.SETPATHdll(os.environ['RPPREFIX'])

fluid = "CARBON DIOXIDE;OXYGEN"
P = 9.5             # MPa
H = 260.49          # kJ/kg
z = [0.89243, 0.10757]

UNITS = RP.GETENUMdll(0, "MASS SI").iEnum
iMass = 1           # 0 = molar basis, 1 = mass basis
iFlag = 1           # THIS IS NEEDED

result = RP.REFPROPdll(fluid, "PH", "T", UNITS, iMass, iFlag, P, H, z)
D = RP.REFPROPdll(fluid, "PH", "D", UNITS, iMass, iFlag, P, H, z)
V = RP.REFPROPdll(fluid, "PH", "V", UNITS, iMass, iFlag, P, H, z)
E = RP.REFPROPdll(fluid, "PH", "E", UNITS, iMass, iFlag, P, H, z)
S = RP.REFPROPdll(fluid, "PH", "S", UNITS, iMass, iFlag, P, H, z)
QMASS = RP.REFPROPdll(fluid, "PH", "QMASS", UNITS, iMass, iFlag, P, H, z)

print(f"Temperature: {result.Output[0]} {result.hUnits}")
print(f"Pressure: {P} MPa")
print(f"Density: {D.Output[0]} {D.hUnits}")
print(f"Volume: {V.Output[0]} {V.hUnits}")
print(f"Int. Energy: {E.Output[0]} {E.hUnits}")
print(f"Enthalpy: {H} kJ/kg")
print(f"Entropy: {S.Output[0]} {S.hUnits}")
print(f"Quality: {QMASS.Output[0]} {QMASS.hUnits}\n")

print(f"ierr: {result.ierr}")
print(f"herr: {result.herr}")

Temperature: 289.4294724600959 K
Pressure: 9.5 MPa
Density: 664.8248961506185 kg/m^3
Volume: 0.001504155463777106 m^3/kg
Int. Energy: 246.20050916957558 kJ/kg
Enthalpy: 260.49 kJ/kg
Entropy: 1.6665341290864955 (kJ/kg)/K
Quality: 0.04142898160603554 -

ierr: 0
herr: 

[BboyArrow1]

Thank you very much for taking the time to reply despite your busy schedule. I would like to continue asking: Is there a better way to call C++?

[Matthew-Boyd]

The best wrappers we have for C and C++ are located here:
https://github.com/usnistgov/REFPROP-cpp-wrapper