An injector, ejector, steam ejector or steam injector is a pump-like device that uses the
Venturi effectof a converging-diverging nozzle to convert the pressureenergy of a motive fluid to velocityenergy which creates a low pressure zone that draws in and entrains a suction fluid and then recompresses the mixed fluids by converting velocity energy back into pressure energy. The motive fluid may be a liquid, steam or any other gas. The entrained suction fluid may be a gas, a liquid, a slurry, or a dust-laden gas stream. [cite book|author=Perry, R.H. and Green, D.W. (Editors)|title= Perry's Chemical Engineers' Handbook|edition=8th Edition|publisher=McGraw Hill|year=2007|id=ISBN 0-07-142294-3] [cite book|author=Power, Robert B.|title=Steam Jet Ejectors For The Process Industries|edition=First Edition|publisher=McGraw-Hill|year=1993|id=ISBN 0-07-050618-3]
The adjacent diagram depicts a typical modern ejector or injector. It consists of a motive fluid inlet nozzle and a converging-diverging outlet nozzle.
Water, air, steam, or any other fluid at high pressure provides the motive force at the inlet.
The Venturi effect, a particular case of
Bernoulli's principle, applies to the operation of this device. Fluid under high pressure is converted into a high-velocity jet at the throat of the convergent-divergent nozzle which creates a low pressure at that point. The low pressure draws the suction fluid into the convergent-divergent nozzle where it mixes with the motive fluid.
In essence, the pressure energy of the inlet motive fluid is converted to
kinetic energyin the form of velocity head at the throat of the convergent-divergent nozzle. As the mixed fluid then expands in the divergent diffuser, the kinetic energy is converted back to pressure energy at the diffuser outlet in accordance with Bernoulli's principle.
Depending on the specific application, an injector is commonly also called an "
Eductor-jet pump, a water eductor", a "vacuum ejector", a "steam-jet ejector", or an " aspirator".
Key design parameters
The compression ratio of the injector, , is defined as ratio of the injectors's outlet pressure to the inlet pressure of the suction fluid .
The entrainment ratio of the injector, , is defined as the amount of motive fluid (in kg/hr) required to entrain and compress a given amount (in kg/hr) of suction fluid..
The compression ratio and the entrainment ratio are key parameters in designing an injector or ejector.
The injector was invented by a Frenchman,
Henri Giffardin 1858 [cite book|author=Strickland L. Kneass|title=Practice and Theory of the Injector|edition=|publisher=John Wiley & Sons (Reprinted by Kessinger Publications, 2007 )|year=1894|id=ISBN 0-548-47587-3] and patented in the United Kingdomby Messrs Sharp Stewart & Co. of Glasgow. Motive forcewas provided at the inlet by a suitable high-pressure fluid.
The injector was originally used in the boilers of
steam locomotives for injecting or pumping the boiler feedwater to and from the boiler. The injector consisted of a body containing a series of three or more nozzles, "cones" or "tubes". The motive steam passed through a nozzle that reduced its pressure below atmospheric and increased the steam velocity. Fresh water was entrained by the steam jet, and both steam and water entered a convergent "combining cone" which mixed them thoroughly so that the water condensed the steam. The condensate mixture then entered a divergent "delivery cone" which slowed down the jet, and thus built up the pressure to above that of the boiler. An overflow was required for excess steam or water to discharge, especially during starting. There was at least one check valvebetween the exit of the injector and the boiler to prevent back flow, and usually a valve to prevent air being sucked in at the overflow.
After some initial skepticism resulting from the unfamiliar and superficially paradoxical mode of operation, the injector was widely adopted as an alternative to mechanical pumps in steam-driven locomotives. The injectors were simple and reliable, and they were thermally efficient.
Steam locomotives dominated rail transport from the mid 19th century until the mid 20th century, after which they were superseded by diesel and
The use of injectors (or ejectors) in various industrial applications has become quite common due to their relative simplicity and adaptability. For example:
* To inject
chemicalsinto the boiler drums of small, stationary, low pressure boilers. In large, high-pressure modern boilers, usage of injectors for chemical dosing is not possible due to their limited outlet pressures.
thermal power stations, they are used for the removal of the boiler bottom ash, the removal of fly ashfrom the hoppers of the electrostatic precipitators used to remove that ash from the boiler flue gas, and for creating a vacuum pressure in steam turbineexhaust condensers.
* For use in producing a vacuum pressure in
steam jet coolingsystems.
* For the bulk handling of
grainsor other granular or powdered materials.
* The construction industry uses them for pumping
turbidwater and slurries.
Similar devices called
aspirators based on the same operating principle are used in laboratoriesto create a partial vacuum and for medical use in suctionof mucus or bodily fluids.
Multi-stage steam ejectors
In practice, for suction pressure below 100
mbarabsolute, more than one ejector will be used, usually with condensors between the ejector stages. Condensing of motive steam greatly improves ejector set efficiency. Both barometricand shell-and-tube surface condensers are used for this purpose.
Injectors or ejectors are fabricated in
carbon steel, Stainless steel, titanium, PTFE, carbonand other materials.
De Laval nozzle
*cite book|author=J.B. Snell|title=Mechanical Engineering: Railways|edition=|publisher=Arrow Books|year=1973|id=ISBN 0-09-908170-9
*cite book|author=J.T. Hodgson and C.S. Lake|title=Locomotive Management|edition=Tenth Edition|publisher=Tothill Press|year=1954|id=
* [http://www.vacuum-guide.com/vacuum_pump/vacuum_ejector/vacuum_ejector_america.htm vacuum-guide.com Injectors manufacturer directory]
* [http://www.croll.com/_website/pr/vetheory.asp Ejector Pumps and Theory]
* [http://www.kinetic-therm.com/content/view/14/38/lang,en/ Ejectors]
* [http://www.muleshoe-eng.com/sitebuildercontent/sitebuilderfiles/Eductor.pdf Use of Eductor for Lifting Water]
* [http://www.steamengine.com.au/steam/faq/simple/injector/lunkenheimer/index.html 1908 Lunkenheimer Injector Catalog]
* [http://www.venturi-vacuum.com/ Applied Vacuum CC]
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Look at other dictionaries:
injector — INJECTÓR, injectoare, s.n. 1. Aparat care serveşte la injectarea combustibilului lichid sau pulverulent în camera de ardere a unui motor cu ardere internă sau care, la instalaţiile cu focar, serveşte la amestecarea combustibilului cu aerul… … Dicționar Român
Injector — In*ject or, n. 1. One who, or that which, injects. [1913 Webster] 2. (Mach.) A contrivance for forcing feed water into a steam boiler by the direct action of the steam upon the water. The water is driven into the boiler by the impulse of a jet of … The Collaborative International Dictionary of English
injector — |ètô| adj. 1. Que injeta. • s. m. 2. Aparelho para injeções. Aparelho para a sulfuração das vinhas. 3. Acessório das máquinas a vapor, destinado à alimentação das caldeiras. ♦ [Portugal] Grafia de injetor antes do Acordo Ortográfico de 1990.… … Dicionário da Língua Portuguesa
injector — [in jek′tər] n. a person or thing that injects, as a device for injecting pressurized fuel into a combustion chamber or for injecting water into a steam boiler … English World dictionary
injector — Refers to the pump system (used in a fuel injection system) that squirts or injects a measured amount of gasoline into the intake manifold in the vicinity of the intake valve. In the diesel engine fuel is injected directly into the cylinder. In a … Dictionary of automotive terms
injector — /in jek teuhr/, n. 1. a person or thing that injects. 2. Mach. a. a device for injecting feedwater into a boiler against high pressure by means of a jet of steam. b. Also called fuel injector. a mechanism consisting of a pump, valves, and nozzles … Universalium
injector — A device to introduce, meter, and atomize the flow of fuel into the air flowing into a combustion chamber. The fuel is propelled into the combustion chamber under pressure other than atmospheric. Simplex fuel injector … Aviation dictionary
injector — injektorius statusas T sritis fizika atitikmenys: angl. injector vok. Injektor, m rus. инжектор, m pranc. injecteur, m … Fizikos terminų žodynas
injector — inject ► VERB 1) introduce into the body with a syringe. 2) administer a drug or medicine to (a person or animal) with a syringe. 3) introduce or feed under pressure into another substance. 4) introduce (a new or different element). DERIVATIVES… … English terms dictionary
injector — noun see inject … New Collegiate Dictionary