Tuesday, July 16, 2013

How Does An Air Ejector Work?


How Does An Air Ejector Work?
written by: Ricky • edited by: Lamar Stonecypher • updated: 6/17/2010
An air ejector or steam ejector is a device which uses the motion of moving fluid (Motive Fluid) to transport another fluid (Suction fluid). It is has a wide range of application in steam ejector in boiler condenser, fresh water generator and in priming the centrifugal pump.
Air Ejector Theory
It works on the principle of convergent /divergent nozzle as it provides the venturi effect at the point of diffusion as the tube gets narrows at the throat the velocity of the fluid increases and because of the venturi affect it pressure decreases, vacuum will occur in the diffuser throat where the suction line will be provided.

An air ejector which uses the high pressure motive fluid such as air or steam to flow through the convergent nozzle the function of the convergent nozzle is to convert the pressure energy of the motive fluid into the velocity energy.

As in convergent nozzle the following effect takes place,




P1-pressure of the fluid entering the nozzle.

V1- velocity of the fluid entering the nozzle.

P2- pressure of the fluid leaving the nozzle.

V2- velocity of the fluid leaving the nozzle.


By Bernoulli’s theorem:

P1 × V1 = P2 × V2.

As the pressure energy before entering the convergent nozzle is greater and the velocity is less for the fluid. At the point of discharge the pressure energy is converted into the velocity so the velocity will be greater and the pressure will be less during the discharge.

Divergent nozzle the opposite effect takes place velocity energy is convert into pressure energy, at the point of diffusion there is a low pressure or vacuum is created which is used to suck the other fluid for the motion.

In the fig: C- Convergent Nozzle.

D- Divergent Nozzle.

V- venturi Point or Diffuser Point.

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