Steam Turbine with wet expansion

[tlmerbecks]

General

With this PR I would like to submit a new turbine component, which accounts for wet expansion effects using the empirical Baumann correlation.

The expansion of saturated steam (e.g. geothermal or nuclear power applications) inevitably enters the vapour dome and two-phase effects lead to a reduction in the isentropic efficiency. The empirical Baumann rule effectively corrects the dry isentropic turbine efficiency with the average wetness across the turbine.

• Implementation of the SteamTurbine component. I chose to make this a separate component (inheriting from Turbine) to avoid confusion - though the SteamTurbine behaves exactly like a Turbine unless the eta_dry_s attribute is set
• Updated the CoolPropWrapper Q_ph function so that it now returns a meaningful value for Q when the fluid is single phase (i.e. 0.0 for liquid and 1.0 for vapour)

Documentation

This is still work in progress... I was not quite sure what would be the mvp for this

Testing

This is still work in progress... I was thinking to shadow the testing for the regular Turbine component

Comments and suggestions are welcome :)

[pep8speaks]

Hello @tlmerbecks! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file src/tespy/components/turbomachinery/steam_turbine.py:

Line 38:80: E501 line too long (86 > 79 characters)
Line 41:80: E501 line too long (80 > 79 characters)
Line 115:80: E501 line too long (80 > 79 characters)

• In the file src/tespy/components/turbomachinery/turbine.py:

Line 267:13: E124 closing bracket does not match visual indentation

• In the file src/tespy/tools/fluid_properties/wrappers.py:

Line 241:80: E501 line too long (90 > 79 characters)

Comment last updated at 2025-01-26 15:19:14 UTC

[fwitte]

Good day Tristan, and nice to see your suggestions! I will have a closer look later today and give you feedback on the implementation. Best!

[tlmerbecks]

@fwitte I have looked through the changes and agree with the simplification of the residual and the introduction of the calc_eta_s function.

I'll have a look at the remaining tests that are still failing later.

Is there anything else you would like to see added/implemented for this?

[fwitte]

@tlmerbecks, nothing to implement from your side right now, but I'd have two questions. I have implemented additional tests, and was curious about the following:

• the method does not work, if the outlet is near saturation (see the first test case)
• what happens with isentropic or dry fluids, when the expansion path starts at or above two-phase and the expansion would never cross the two-phase boundary? Or, when the expansion starts in saturated vapor and goes into the gas region?

I guess in both cases we could argue, the method is not applicable here? Or we could make a check, where the inlet and the outlet are (two-phase or gas) and depending on that use one or the other method for expansion? What do you think?

[fwitte]

And, should we add a reference to the original research, that would be "Baumann, K.: Some Recent Developments In Large Steam Turbine Practice. Engrg. Vol. Ill (1921)" I guess?

[tlmerbecks]

Ciao @fwitte ,

I have found a quiet moment :) to answer your questions:

The method is only really applicable if the fluid is water, this is because the correction is entirely based on empirical data on the performance of steam turbines. With this is mind, given the shape of water's vapour dome in the Ts domain it is unnecessary to check for retrograde behaviour.

That being said, perhaps the first check should be whether the phase of the fluid is different between the inlet and outlet. So in the case where the outlet conditions are just above saturation, the fluid enters and exits the turbine as vapour so no correct needs to be applied.

So basically what you already suggested :p

As for the reference, the one you gave is the original one used everywhere, though it is not that easy to track down. One other resource that really helped me with this was:

@book{Tanuma2017,
   doi = {10.1016/C2014-0-03636-2},
   editor = {T. Tanuma},
   isbn = {9780081003145},
   publisher = {Elsevier},
   title = {Advances in Steam Turbines for Modern Power Plants},
   year = {2017},
}