The main systems are the Steam (Rankine) Cycle and the Gas Turbine (Brayton Cycle).
- Steam (Rankine) Cycle is an ideal thermodynamic cycle that consists of four processes:
- Heat transfer to the system at constant pressure.
- An expansion at constant entropy.
- A constant-pressure heat transfer from the system.
- A compression at constant entropy; used as a standard of efficiency.
- Gas Turbine (Brayton) Cycle, an ideal gas cycle used as a standard for the actual performance of a simple gas turbine, consisting of four processes:
- A reversible adiabatic (no heat transfer) compression at constant entropy.
- A heat transfer at constant pressure up to the maximum temperature.
- An adiabatic expansion at constant entropy back to the original pressure.
- A heat transfer at constant pressure back to the original volume and entropy.
- Entropy in thermodynamics is a measure of the disorder or randomness of a closed system; more entropy means less energy is available for doing work.
The total entropy of an isolated system cannot decrease when the system undergoes a change; it can remain constant for reversible processes, and will increase for irreversible ones.