Help with Python wrapper

[mwburgoyne]

I am having some 'fun' trying to get expected behaviour via the Python interface and was hoping the community might be able to help me

Starting with what I 'thought' was a simple example, I wanted to calculate the density and viscosity of a 50:50 mixture of methane and CO2 with following code

from ctREFPROP.ctREFPROP import REFPROPFunctionLibrary

refprop_path = r'C:\Program Files (x86)\REFPROP'
RP = REFPROPFunctionLibrary(refprop_path)
RP.SETPATHdll(refprop_path)
RP.SETFLUIDSdll("METHANE;CO2")

MOLAR_SI = RP.GETENUMdll(0,"MOLAR SI").iEnum

T = 237.93
pMPa = 20.08
p_kPa = pMPa * 1000
z = [0.5, 0.5] + [0.0]*18

# 1. Molar density (mol/L)
dens_mol = RP.REFPROPdll("METHANE;CO2", "TP", "D", MOLAR_SI, 0, 0, T, p_kPa, z)
molar_density_mol_L = dens_mol.Output[0]

# 2. Per-component MWs (g/mol)
mw_components = RP.REFPROPdll("METHANE;CO2", "", "MM", MOLAR_SI, 0, 0, 0, 0, z).Output

# 3. Mixture MW (g/mol)
mixture_MW = sum(zi * mwi for zi, mwi in zip(z, mw_components))

# 4. Mass density (kg/m³)
mass_density_kg_m3 = molar_density_mol_L * 1000 * mixture_MW / 1000

# 5. Viscosity (Pa·s and cP)
visc = RP.REFPROPdll("METHANE;CO2", "TP", "ETA", MOLAR_SI, 0, 0, T, p_kPa, z)
viscosity_Pa_s = visc.Output[0]
viscosity_cP = viscosity_Pa_s * 1000

print(f"Molar density: {molar_density_mol_L:.4f} mol/L")
print(f"Mixture MW: {mixture_MW:.4f} g/mol")
print(f"Mass density: {mass_density_kg_m3:.4f} kg/m³")
print(f"Viscosity: {viscosity_cP:.5f} cP")
print("Viscosity ierr:", visc.ierr, "herr:", visc.herr)

However I am getting nonsensical density and viscosity as follows;
Molar density: 67.5875 mol/L
Mixture MW: 30.0263 g/mol
Mass density: 2029.4024 kg/m³
Viscosity: 1435727.29156 cP
Viscosity ierr: 0 herr:

Any idea where I am going wrong?

Using the REFPROP tool itself yields expected results - I just cant get a sensible answer through the Python wrapper

Thanks in advance,

Mark

[mwburgoyne]

Have closed this and reposted in (what I hope) is a more appropriate forum:
#657