Deviation in density calculation

[torlid]

Describe the bug
Significant deviation in density

To Reproduce
The density if gas phase in neqsim : 11.31
The density in Unisim: 11.15

1.4% deviation

The SRK model is used in both unisim and neqsim-python (v 3.0.11)

Should I expect "exact" same result in both Unisim and Neqsim, or is this what I should expect?

Steps to reproduce the behavior:

Gas composition:
component - value [mol%]
nitrogen - 1.09
CO2 - 1.67
methane - 83.48
ethane - 7.36
propane - 3.68
i-butane - 0.59
n-butane - 1.06
i-pentane - 0.28
n-pentane - 0.28
n-hexane - 0.16
water - 0.23
n-heptane - 0.1118
n-octane - 0.0182
T = 30°C
P = 13.813 bar a

Expected behavior
Equal values

[EvenSol]

Thanks for reporting this issue.

I tested the composition you reported with the SRK-EoS and reproduced your results using NeqSim. You can see my discussion in the following notebook:

https://github.com/EvenSol/NeqSim-Colab/blob/master/notebooks/thermodynamics/density_of_gas_using_SRK_EoS.ipynb

I suspect the density difference might be due to minor variations in the critical temperature (Tc), critical pressure (Pc), acentric factor or molecular weight of some components. If anyone could verify these results with other software, it would be helpful. My feeling is that the GERG-2008 EoS should provide the most accurate density calculation for this gas.

[torlid]

Thanks Even, for your reply.
Then I do not have to search for some error in my script :-)
Tore

[nwpro9]

Thanks, Even. Confirming that GERG-2008 provides more consistent gas density for CO2 on my end. Could you show how to modify the Tc, Pc, acentric factor, and molecular weight of components?

[EvenSol]

Hi, good question.

I hope this notebook helps explaining how this can be done:

The notebook demostrates how you you can make your own parameter database or update parameters in program code,

You have two ways:

1. Create a custom parameter database: You can start by copying the existing NeqSim parameter database and then modify it with your desired values. This approach allows you to maintain a separate database for your specific needs.
2. Directly modify parameters in the NeqSim code: This method involves changing the parameter values within the NeqSim program code itself. It can be useful for quick adjustments but might require more advanced understanding of the code structure.