Everything about Nozzle totally explained
A
nozzle is a mechanical device or
orifice designed to
control the characteristics of a
fluid flow as it exits (or enters) an enclosed chamber or pipe.
A nozzle is often a pipe or tube of varying cross sectional area, and it can be used to direct or modify the flow of a fluid (
liquid or
gas). Nozzles are frequently used to control the rate of flow, speed, direction, mass, shape, and/or the pressure of the stream that emerges from them.
Types of nozzles
Jets
A
gas jet,
fluid jet, or
hydro jet is a
nozzle intended to eject gas or fluid in a coherent stream into a surrounding medium. Gas jets are commonly found in
gas stoves,
ovens, or
barbecues. Gas jets were commonly used for
light before the development of
electric light. Other types of fluid jets are found in
carburetors, where smooth
calibrated orifices are used to regulate the flow of
fuel into an engine, and in
jacuzzis or
spas.
High velocity nozzles
Frequently the goal is to increase the
kinetic energy of the flowing medium at the expense of its
pressure energy and/or
internal energy.
Nozzles can be described as
convergent (narrowing down from a wide diameter to a smaller diameter in the direction of the flow) or
divergent (expanding from a smaller diameter to a larger one). A
de Laval nozzle has a convergent section followed by a divergent section and is often called a convergent-divergent nozzle.
Convergent nozzles accelerate subsonic fluids. If the nozzle pressure ratio is high enough the flow will reach sonic velocity at the narrowest point (for example the
nozzle throat). In this situation, the nozzle is said to be
choked.
Increasing the nozzle pressure ratio further won't increase the throat
Mach number beyond unity. Downstream (for example external to the nozzle) the flow is free to expand to supersonic velocities. Note that the Mach 1 can be a very high speed for a hot gas; since the
speed of sound varies as the square root of absolute temperature. Thus the speed reached at a nozzle throat can be far higher than the speed of sound at sea level. This fact is used extensively in rocketry where
hypersonic flows are required, and where propellant mixtures are deliberately chosen to further increases the sonic speed.
Divergent nozzles slow fluids, if the flow is subsonic, but accelerate sonic or supersonic fluids.
Convergent-divergent nozzles can therefore accelerate fluids that have choked in the convergent section to supersonic speeds. This CD process is more efficient than allowing a convergent nozzle to expand supersonically externally.
The shape of the divergent section also ensures that the direction of the escaping gases is directly backwards, as any
sideways component wouldn't contribute to thrust.
A jet exhaust produces a net thrust due to the energy obtained from combusting fuel which is added to the inducted air, increasing its kinetic energy.
For a given mass flow, greater thrust is obtained with a higher exhaust velocity. However, the best energy efficiency is obtained when the exhaust speed is well matched with the airspeed, but greater mass flows are needed to give similar thrust. However, no jet aircraft can fly exceed its exhaust jet speed very much due momentum considerations, and so supersonic jet engines, like those employed in
fighters and
SST aircraft (for example Concorde), need high exhaust speeds which in turn implies relatively high nozzle pressure ratios. Therefore supersonic aircraft very typically use a CD nozzle despite weight and cost penalties. Subsonic jet engines employ relatively low, subsonic, exhaust velocities. They thus have modest nozzle pressure ratios and employ simple convergent nozzles. In addition,
bypass nozzles are employed giving even lower speeds.
Rocket motors use convergent-divergent nozzles with very large area ratios so as to maximise thrust and exhaust velocity and thus extremely high nozzle pressure ratios are employed. Mass flow is at a premium since all the propulsive mass is carried with vehicle, and the very highest exhaust speeds are usually desirable.
Nozzles used on feeding
hot blast in a
blast furnace or
forge are called
tuyeres.
Magnetic nozzles
Magnetic nozzles have also been proposed for some types of propulsion, such as
VASIMR, in which the flow of
plasma is directed by
magnetic fields instead of walls made of solid matter.
Spray nozzles
Many nozzles "atomise" liquids.
Air-Aspirating Nozzle-uses an opening in the cone shaped nozzle to inject air into a stream of water based foam (CAFS/AFFF/FFFP) to make the concentrate "foam up". Most commonly found on foam extinguishers and foam handlines.
Swirl nozzles inject the liquid in tangentially, and it spirals into the center and then exits through the central hole. Due to the vortexing this causes the spray to come out in a cone shape.
Vacuum nozzles
Vacuum cleaner nozzles come in several different shapes.
Shaping nozzles
Some nozzles are shaped to produce a stream that's of a particular shape. For example Extrusion molding is a way of producing lengths of metals or plastics or other materials with a particular cross-section. These nozzles are typically referred to as a die.
Other meanings
In some areas of Scotland, the nozzle can refer to the nose.
Further Information
Get more info on 'Nozzle'.
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