Editing Steam engine (section)

=== Cold sink ===
As with all heat engines, the majority of [[primary energy]] must be emitted as [[waste heat]] at relatively low temperature.<ref name="energy.gov">{{cite web|url=http://fossil.energy.gov/programs/powersystems/turbines/turbines_howitworks.html |title=Fossil Energy: How Turbine Power Plants Work |publisher=Fossil.energy.gov |access-date=2011-09-25 |url-status=dead |archive-url=https://web.archive.org/web/20110812012523/http://fossil.energy.gov/programs/powersystems/turbines/turbines_howitworks.html |archive-date=12 August 2011 }}</ref>

The simplest cold sink is to vent the steam to the environment. This is often used on [[steam locomotive]]s to avoid the weight and bulk of condensers. Some of the released steam is vented up the chimney so as to increase the draw on the fire, which greatly increases engine power, but reduces efficiency.

Sometimes the waste heat from the engine is useful itself, and in those cases, very high overall efficiency can be obtained.

Steam engines in stationary power plants use [[surface condenser]]s as a cold sink. The condensers are cooled by water flow from oceans, rivers, lakes, and often by [[cooling tower]]s which evaporate water to provide cooling energy removal. The resulting condensed hot water (''condensate''), is then pumped back up to pressure and sent back to the boiler. A dry-type cooling tower is similar to an automobile radiator and is used in locations where water is costly. Waste heat can also be ejected by evaporative (wet) cooling towers, which use a secondary external water circuit that evaporates some of flow to the air.

River boats initially used a [[jet condenser]] in which cold water from the river is injected into the exhaust steam from the engine. Cooling water and condensate mix.  While this was also applied for sea-going vessels, generally after only a few days of operation the boiler would become coated with deposited salt, reducing performance and increasing the risk of a boiler explosion.  Starting about 1834, the use of surface condensers on ships eliminated fouling of the boilers, and improved engine efficiency.<ref>Nick Robins, ''The Coming of the Comet: The Rise and Fall of the Paddle Steamer'', Seaforth Publishing, 2012, {{ISBN|1-4738-1328-X}}, Chapter 4</ref>

Evaporated water cannot be used for subsequent purposes (other than rain somewhere), whereas river water can be re-used. In all cases, the steam plant boiler feed water, which must be kept pure, is kept separate from the cooling water or air.

[[File:Boiler Feed Injector Diagram.svg|thumb|right|An [[injector]] uses a jet of steam to force water into the boiler. Injectors are inefficient but simple enough to be suitable for use on locomotives.]]