PhaseType Function result incorrect in Peng Robinson

[alkanism]

Function PhaseType in PengRobinson.vb returns a phase type of "L" for a gas composition I have.

The gas composition I have and its properties are in the attached screenshot files.
This should really be a gas composition in a gaseous state.

I tested this in a file where only an Input stream is defined; nothing else. And Peng Robinson is the EOS selected.

I believe the problem is originating from the following lines which compute the compressibility factor (as a very small number instead of 1.0003)
_zarray = CalcZ(T, P, Vx, VKij, VTc, VPc, Vw)
_mingz = ZtoMinG(_zarray.ToArray(), T, P, Vx, VKij, VTc, VPc, Vw)
Z = _zarray(_mingz(0))

This block of code is also used in ReturnParameters function and elsewhere too.
Because of that the CalcJouleThamsonCoefficient and CalcIsothermalCompressibility functions might be calculating incorrect values as well.

My OS is Windows 11 Pro
DWSIM version I am using is 8.8.2

[DanWBR]

@alkanism try checking this box in the settings window:

[alkanism]

That doesn't help. It actually produces results all wrong. Now it thinks that this composition is liquid, which can't be right.
The gas composition I have above is already in an equilibrium state anyway (it's a flue gas composition from gas turbine)

Without the checkbox checked, all results were good except PhaseType function result was wrong (returning "L") as the mixture type and similarly, JouleThomsonCoefficient and IsothermalCompressibility were likely wrong because of the incorrect compressibility factor calculated within those routines.
The compressibility factor and all other properties were being calculated correctly without checking the box.

[DanWBR]

@alkanism you can force the stream phase or try another property package like GERG-2008.

[alkanism]

Thanks for your prompt responses Daniel.

I force the stream to be a vapor, and I get the original correct results I posted.

But, as I mentioned before, I believe JouleThomsonCoefficient and IsothermalCompressibility results are wrong due to incorrect calculation of Z inside those routines. Even though it's not used, PhaseType function result will still be incorrect as well.

Of course I can use some other EOS; my purpose of reporting this was to alert you.

[DanWBR]

@alkanism, yes, I know. The problem is that PR/SRK behaves very weirdly at higher temperatures and pressures. There are algorithms to "fix" the calculation of Z, but I couldn't get one to work properly without slowing down the calculations for everyone.

[DanWBR]

@alkanism thanks for reporting.