injector

For other uses, see Injector (disambiguation) and Ejector (disambiguation).

Diagram of a typical modern ejector.

An injector, ejector, steam ejector, steam injector, eductor-jet pump or thermocompressor is a pump-like device that uses the Venturi effect of a converging-diverging nozzle to convert the pressure energy of a motive fluid to velocity energy which creates a low pressure zone that draws in and entrains a suction fluid. After passing through the throat of the injector, the mixed fluid expands and the velocity is reduced which results in recompressing 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.^[1][2]
The adjacent diagram depicts a typical modern ejector. 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.
An injector is a more complex device containing at least three cones. That used for delivering water to a steam locomotive boiler takes advantage of the release of the energy contained within the latent heat of evaporation to increase the pressure to above that within the boiler.
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 energy in 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.

Contents

[hide]

• 1 Key design parameters
• 2 History
  • 2.1 Feedwater injectors
  • 2.2 Vacuum ejectors
• 3 Modern uses
• 4 Well Pumps
• 5 Multi-stage steam ejectors
• 6 Construction materials
• 7 See also
• 8 References
• 9 Additional reading
• 10 External links