What is a Rankine cycle process?

Rankine cycle is the ideal cycle for vapor power plants and consists of the following four processes:

1-2 Isentropic compression in a pump
2-3 Constant pressure heat addition in a boiler
3-4 Isentropic expansion in a turbine
4-1 Constant pressure heat rejection in a condenser

 Water enters the pump at state 1 as saturated liquid and is compressed isentropically to the operating     pressure of the boiler. There is slight increase in water temperature during the compression process.

Water enters the boiler as a compressed liquid at state 2 and leaves as a superheated vapor at state 3. The boiler is basically a heat exchanger where water is heated at constant pressure.

The superheated vapor at state 3 enters the turbine, where it expands isentropically and produces work by rotating shaft connected to an electric generator. The pressure and the temperature of the steam drop during this process to the values at state 4.

Steam enters the condenser at state 4. At this state steam is usually a saturated liquidvapor mixture with a high quality. It is condensed at constant pressure and leaves the condenser as a saturated liquid.