Thermal Efficiency and Isentropic Efficiency
In Chapters 4 and 5 we defined the thermal efficiency of a cycle as:
- We want to define a new efficiency that can be used to evaluate the performance of a single process such as a pump, compressor, turbine, or even a nozzle.
- The thermal efficiency is based on the comparison of the performance of a real cycle to the performance of a hypothetical cycle which could convert heat completely into work.
- This hypothetical cycle violates the 2nd Law.
In Chapter 6, we learned that a Carnot Cycle has the maximum thermal efficiency and we showed that for any Carnot Cycle:
- In order to develop an efficiency for individual processes, we will compare the performance of real, irreversible processes to the performance of isentropic processes (adiabatic and internally reversible ).
We will call this new type of efficiency the
isentropic efficiencyand it will be represented by ηs
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