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Air ejector .pdf



Original filename: Air ejector.pdf
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Air Ejector works on the principle of convergent or 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.

Air ejectors on a ship help in removing air blocks from the ship's feed water system. There are
several types of air ejectors used on ships. The article describes as to how an air ejector works
and what are its important parts are. Removing any amount of trapped air from working systems
on a ship is an essential task. Trapped air is mainly found in systems which deal with carrying
steam and vapours. Air in the system not only leads to loss of differential pressure across the
system but also to many harmful conditions in the long term. One such system on ship wherein
air is commonly found is the feed water system. To eradicate the problem of trapped air from
feed water system, air ejectors are used.

Air ejector is an essential component of any type of feed system on the ship. As the name
suggests, the equipment completely removes the air from any system and also draws out the
vapours released from the condensing steam in the condenser.

Presence of air in the system leads to several detrimental effects on the boiler. Corrosion is one
such effect that in long run results is failure of the boiler from the inside. Also, the accumulation
of air inside the condenser affects the condensing process, which results in the production of
back pressure. The back pressure thus generated leads to increase in exhaust steam pressure and
reduction in thermal efficiency of the plant.

All ejectors operate on a common principle. They entrain air or other fluids in a high velocity jet
of propelling air, steam, water or other fluid. And they use the kinetic energy in the high velocity
stream of that fluid to push back the atmosphere from the discharge of the ejector. This would
suggest that the higher the velocity of the jet from the nozzle of the ejector, the greater the
pressure against which the ejector can exhaust or if the exhaust pressure remains constant, the
higher the vacuum produced by the ejector. This is true and for any particular velocity of the jet
there is, of course, a limit to the vacuum that can be produced.

A steam ejector basically comprises of three (3) elements: a nozzle, a mixing chamber and a
diffuser. A high pressure motive fluid, typically steam, enters the steam ejector and passes
through the nozzle. Through this nozzle, its velocity increases and consequently low pressure
exists at that point on nozzle. This low pressure draws the suction fluid, typically air, into the
mixing chamber where it mixes with the motive fluid. The mixture then passes through the
diffuser. There, the mixed fluid expands, its velocity is reduced and its pressure is increased,
resulting in recompressing the mixed fluids by converting velocity energy back into pressure
energy.
A new development in steam ejectors technology is the advent of hybrid air ejectors. This is
actually a combination of an air jet ejector and a vacuum pump. The air ejector is installed at the
suction of the vacuum pump, thus boosting its suction pressure and thus reducing the capitalinvestment cost for this pump. This first-stage ejector also helps minimize pump cavitation, as

the pump no longer operates at low suction pressures, which could lead to vaporization of the
seal liquid in the pump casing.
Crystal TCS is a niche technology based engineering firm working in the field of Ejector based
Vacuum systems, Corrosion resistant Equipment and Hydrogen Generation Systems.
Understanding the needs of the customer along with Technology and Manufacturing excellence
are our prime assets when it comes to satisfying the diverse demands of the industry.
For more information please contact us or call on +912532501600 / 9921391762
http://www.crystaltcs.com/vacuum-systems.php


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