Editing Rankine cycle (section)

== The four processes in the Rankine cycle ==
[[File:Rankine cycle Ts.png|class=skin-invert-image|thumb|upright=1.6|[[T–s diagram]] of a typical Rankine cycle operating between pressures of 0.06&nbsp;bar and 50&nbsp;bar. Left from the bell-shaped curve is liquid, right from it is gas, and under it is saturated liquid–vapour equilibrium.]]
There are four processes in the Rankine cycle. The states are identified by numbers (in brown) in the [[T–s diagram]].

{|class="wikitable"
|+Successive processes of the Rankine cycle
!width=90px|Name!!Summary!!Explanation
|-
|Process 1–2||[[Isentropic]] compression||The working fluid is pumped from low to high pressure. As the fluid is a liquid at this stage, the pump requires little input energy.
|-
|Process 2–3||Constant pressure heat addition in boiler||The high-pressure liquid enters a boiler, where it is heated at constant pressure by an external heat source to become a dry saturated vapour. The input energy required can be easily calculated graphically, using an [[enthalpy–entropy chart]] ([[h–s chart]], or [[Mollier diagram]]), or numerically, using [[steam table]]s or software.
|-
|Process 3–4||Isentropic expansion||The dry saturated vapour expands through a [[turbine]], generating power. This decreases the temperature and pressure of the vapour, and some condensation may occur. The output in this process can be easily calculated using the chart or tables noted above.
|-
|Process 4–1||Constant pressure heat rejection in condenser||The wet vapour then enters a [[Surface condenser|condenser]], where it is condensed at a constant pressure to become a [[Boiling point|saturated liquid]].
|}

In an ideal Rankine cycle the pump and turbine would be isentropic: i.e., the pump and turbine would generate no entropy and would hence maximize the net work output. Processes 1–2 and 3–4 would be represented by vertical lines on the [[T–s diagram]] and more closely resemble that of the [[Carnot cycle]]. The Rankine cycle shown here prevents the state of the working fluid from ending up in the superheated vapor region after the expansion in the turbine,
{{ref label | Van_Wyllen |1| a}} which reduces the energy removed by the condensers.

The actual vapor power cycle differs from the ideal Rankine cycle because of irreversibilities in the inherent components caused by fluid friction and heat loss to the surroundings; fluid friction causes pressure drops in the boiler, the condenser, and the piping between the components, and as a result the steam leaves the boiler at a lower pressure; heat loss reduces the net work output, thus heat addition to the steam in the boiler is required to maintain the same level of net work output.