Steam Turbines Part-Load Isentropic Efficiency

Dear Sirs,

I reviewed in SAM, Type 234.for file, related to Balance of Plant power calculations, and I noticed Steam Turbine Isentropic Efficiency is a Fixed value: 88%.

I would like to know if you considered to introduce a correction factor to simulate steam turbines with part-load conditions. I think under part-load conditions steam turbines isentropic efficiency is not a Fixed value, as programmed, I suppose it could vary according to inlet steam flow, the so called 'flow factor'.

Best Regards,

Luis Coco

Hello Luis,

You're correct that the isentropic efficiency varies as a function of turbine load. We've modeled the efficiency to have dependence on mass flow fraction (flow factor - as you mentioned). In Type 234, the turbine efficiency 'eta_t' is equal to the design point isentropic efficiency (0.88) times a flow-based correction factor as defined in the function 'eta_pl(...)'. The efficiency correction is:

eta_pl = 1.-(0.191-0.409*mf + 0.218*mf**2.)

where 'mf' is the flow rate relative to the design-point mass flow rate.

Best,
Mike Wagner
NREL

Thank you very much Michael for your response. I found in Type 234
the code the formula according Patnode thesis.

I would like to ask you if you know same Isentropic Efficiency formula
for Supercritical Carbon Dioxide Turbines and Compressors.

Best Regards,

Luis Coco

Dear Luis,

The off-design modeling work that we are most familiar with is from John Dyreby at UW-Madison. His paper from the 2011 Supercritical CO2 Power Cycle Symposium ("Modeling Off-Design Operation of a Supercritical Carbon Dioxide Brayton Cycle") describes his turbo-machinery modeling. His compressor model uses dimensionless flow and ideal head coefficients, and he presents of comparison of his model and data measured at Sandia National Laboratories. He also presents a standard gas turbine off-design relationship, but presently there are no public experimental data for comparison.

Best regards,
Paul.

Dear Paul and Michael, first of all thank you very again for your help.