The simplest steam power cycle consists of
four changes of state:
1–2: Liquid pressurised water is evaporated in a
boiler by input of heat
2–4: The steam expands associated with
mechanical power output. In power plants
the mechanical energy is transformed into
electrical energy by a generator.
4–5: The expanded steam is condensed to water
with associated heat output
5–1: The condensed water is pressurised by a feed
pump and delivered back into the boiler