Editing Injector (section)

==History==
===Giffard===
The injector was invented by [[Henri Giffard]] in early 1850s and patented in France in 1858, for use on [[steam locomotive]]s.<ref>{{cite book|author=Strickland L. Kneass|title=Practice and Theory of the Injector|url=https://archive.org/details/practiceandtheo04kneagoog|publisher=John Wiley & Sons (Reprinted by Kessinger Publications, 2007 )|year=1894|isbn=978-0-548-47587-4}}</ref> It was patented in the [[United Kingdom]] by [[Sharp, Stewart and Company]] of [[Glasgow]].

After some initial scepticism resulting from the unfamiliar and superficially paradoxical mode of operation,<ref name="k1910">{{cite book |author=[[Strickland Landis Kneass]] |title=Practice and Theory of the Injector |publisher=John Wiley & Sons (Reprinted by Wentworth Press, 2019) |year=1910 |isbn=978-0469047891}}</ref>{{rp|5}} the injector became widely adopted for steam locomotives as an alternative to mechanical pumps.{{r|k1910|p=5,7}}

===Kneass===
[[Strickland Landis Kneass]] was a [[civil engineer]], experimenter, and author, with many accomplishments involving railroading.<ref>{{cite journal |last1=Graff |first1=Frederic |title=Obituary Notice of Strickland Kneass |journal=Proceedings of the American Philosophical Society |date=April 1884 |volume=21 |issue=115 |pages=451–455 |jstor=982738 |url=https://www.jstor.org/stable/982738 |access-date=September 22, 2023}}</ref>  Kneass began publishing a mathematical model of the physics of the injector, which he had verified by experimenting with steam.  A steam injector has three primary sections:<ref name="k1910"/>

*Steam nozzle, a diverging duct, which converts high pressure steam to low pressure, high velocity wet steam
*Combining tube, a converging duct, which mixes high velocity steam and cold water
*Delivery tube, a diverging duct, where a high velocity stream of steam and cold water become a slow high pressure stream of water

====Nozzle====
[[File:Kneass15steamDischarge.png|thumb|right|Kneass's illustrations of differently shaped steam nozzles]]
Figure 15 shows four sketches Kneass drew of steam passing through a nozzle.  In general, [[compressible flow]]s through a diverging duct increase velocity as a gas expands.  The two sketches at the bottom of figure 15 are both diverging, but the bottom one is slightly curved, and produced the highest velocity flow parallel to the axis.  The area of a duct is proportional to the square of the diameter, and the curvature allows the steam to expand more linearly as it passes through the duct.

An [[ideal gas]] cools during [[adiabatic]] expansion (without adding heat), releasing less energy than the same gas would during [[isothermal]] expansion (constant temperature).  Expansion of steam follows an intermediate [[thermodynamic process]] called the [[Rankine cycle]].  Steam does more [[Work (thermodynamics)|work]] than an ideal gas, because steam remains hot during expansion.

The extra heat comes from [[enthalpy of vaporization]], as some of the steam condenses back into droplets of water intermixed with steam.<ref name="k1910"/>

====Combining tube====
At the end of the nozzle, the steam has very high velocity, but at less than atmospheric pressure, drawing in cold water which becomes [[Entrainment (hydrodynamics)|entrained]] in the stream, where the steam condenses into droplets of water in a converging duct.

====Delivery tube====
The delivery tube is a diverging duct where the force of deceleration increases pressure, allowing the stream of water to enter the boiler.