Question Regarding Ideal Gas Assumption in IsentropicNozzle Function

[Shawn-W357]

Hello,
I’ve been reading the IsentropicNozzle function in your code (/PDSim/flow/flow_models.pyx, line 618).

I noticed that thermodynamics (e.g. Cp) are extracted using CoolProp, which provides real gas data. However, the subsequent calculations (e.g. k and rho) are based on ideal gas assumption.
This makes me wonder:

1. How does this approach affect the accuracy of the results, particularly when the gas behavior deviates from ideal conditions?
2. Is the enthalpy also calculated using CoolProp?
3. Can the error introduced by this method be considered negligible in engineering design issues？

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P (Pa)	T (K)	rho (kg/m^3)		R
		p/(RT)	CoolProp	114.56
1.40E+06	305	4.01E+01	49.58344567
1.80E+06	320	4.91E+01	61.93591356

In my case study, I found that the density calculated using rho = p/(R*T) differs nearly 20% from that provided by CoolProp.
I would really appreciate your insights on these points. Thank you for your time.

Best regards.

[ibell]

It's a good question - things get messy indeed if you don't make this assumption. The next step is the compressible real gas flow, and that is SLOW because you need to do multiple calls along the path. See my paper about the corrected nozzle flow for a flavor. Getting the density from the EOS would be very easy - not sure why I used the ideal-gas one. But I am not sure what impact that has on the results. Ultimately, the "right" answer is what gives the closest agreement with the experimental mass flows in the compressor

[Shawn-W357]

Thank you for your reply.