Compares real turbine or compressor work with the ideal reversible one.
η_turbine=(h₁-h₂)/(h₁-h₂s) and η_compressor=(h₂s-h₁)/(h₂-h₁) compare real devices to the isentropic ideal. Typical 80–90%. Irreversibility (friction, turbulence, heat loss) raises exit enthalpy or entropy.
A turbine with isentropic exit h=2400 and efficiency 85% from h=3200 exits at h=2520 kJ/kg.
Isentropic efficiency tells you how far a real turbine or compressor falls short of the ideal reversible machine, which is a key performance check.
Compares real turbine or compressor work with the ideal reversible one.
Isentropic efficiency tells you how far a real turbine or compressor falls short of the ideal reversible machine, which is a key performance check.
The actual work output divided by the ideal isentropic work for the same inlet state and exit pressure.
Large turbines can reach around 90 percent, while small machines often have lower values because of larger relative losses.
Typical applications include checking whether a turbine has lost too much work due to blade wear, comparing two compressors at the same pressure ratio and estimating the outlet temperature of a compressor after a real compression.
Study "T-s diagrams" first (topic 26 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Isentropic exit state first. Polytropic efficiency. Nozzle efficiency.
A turbine with isentropic exit h=2400 and efficiency 85% from h=3200 exits at h=2520 kJ/kg.
The next topic is "Exergy", which builds directly on this one.
It is classed as Beginner in Thermodynamics & Fluids (topic 27 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.