Editing Steam engine (section)

== Steam cycle ==
{{Main|Rankine cycle}}
{{See also|Thermodynamics|Heat transfer}}

[[File:Rankine cycle layout.png|thumb|upright=1.35|Flow diagram of the four main devices used in the [[Rankine cycle]]. 1)&nbsp;Feedwater pump 2)&nbsp;Boiler or steam generator 3)&nbsp;Turbine or engine 4)&nbsp;Condenser; where ''Q''=heat and ''W''=work. Most of the heat is rejected as waste.]]
The Rankine cycle is the fundamental thermodynamic underpinning of the steam engine. The cycle is an arrangement of components as is typically used for simple power production, and uses the phase change of water (boiling water producing steam, condensing exhaust steam, producing liquid water)) to provide a practical heat/power conversion system. The heat is supplied externally to a closed loop with some of the heat added being converted to work and the waste heat being removed in a condenser. The Rankine cycle is used in virtually all steam power production applications. In the 1990s, Rankine steam cycles generated about 90% of all electric power used throughout the world, including virtually all [[solar thermal|solar]], [[biomass]], [[Coal power|coal]], and [[Nuclear power|nuclear]] [[power plant]]s. It is named after [[William John Macquorn Rankine]], a Scottish [[polymath]].<ref>{{Cite web |title=William J. M. Rankine |url=https://engineeringhalloffame.org/profile/william-j-m-rankine |access-date=2022-12-13 |website=Scottish Engineering Hall of Fame |language=en}}</ref>

The Rankine cycle is sometimes referred to as a practical [[Carnot cycle]] because, when an efficient turbine is used, the [[TS diagram]] begins to resemble the Carnot cycle. The main difference is that heat addition (in the boiler) and rejection (in the condenser) are [[Isobaric process|isobaric]] (constant pressure) processes in the Rankine cycle and [[Isothermal process|isothermal]] (constant [[temperature]]) processes in the theoretical Carnot cycle. In this cycle, a pump is used to pressurize the working fluid which is received from the condenser as a liquid not as a gas. Pumping the working fluid in liquid form during the cycle requires a small fraction of the energy to transport it compared to the energy needed to compress the working fluid in gaseous form in a compressor (as in the [[Carnot cycle]]).<!-- check-the source was too ambiguous--> The cycle of a reciprocating steam engine differs from that of turbines because of condensation and re-evaporation occurring in the cylinder or in the steam inlet passages.{{sfn|Hunter|1985|p=445}}

The working fluid in a Rankine cycle can operate as a closed loop system, where the working fluid is recycled continuously, or may be an "open loop" system, where the exhaust steam is directly released to the atmosphere, and a separate source of water feeding the boiler is supplied. Normally water is the fluid of choice due to its favourable properties, such as non-toxic and unreactive chemistry, abundance, low cost, and its [[Properties of water#Heat capacity and heats of vaporization and fusion|thermodynamic properties]]. [[Mercury (element)|Mercury]] is the working fluid in the [[mercury vapor turbine]]. Low boiling hydrocarbons can be used in a [[binary cycle]].<ref>{{Cite web |last=Parada |first=Angel Fernando Monroy |date=2013 |title=GEOTHERMAL BINARY CYCLE POWER PLANT PRINCIPLES, OPERATION AND MAINTENANCE |url=https://orkustofnun.is/gogn/unu-gtp-report/UNU-GTP-2013-20.pdf |access-date=2022-12-13 |website=Orkustofnun (Islandic National Energy Authority)}}</ref>

The steam engine contributed much to the development of thermodynamic theory; however, the only applications of scientific theory that influenced the steam engine were the original concepts of harnessing the power of steam and atmospheric pressure and knowledge of properties of heat and steam. The experimental measurements made by Watt on a model steam engine led to the development of the separate condenser. Watt independently discovered [[latent heat]], which was confirmed by the original discoverer [[Joseph Black]], who also advised Watt on experimental procedures. Watt was also aware of the change in the boiling point of water with pressure. Otherwise, the improvements to the engine itself were more mechanical in nature.{{sfn|Landes|1969|p=}} The thermodynamic concepts of the Rankine cycle did give engineers the understanding needed to calculate efficiency which aided the development of modern high-pressure and -temperature boilers and the steam turbine.{{Citation needed|date=February 2020}}