Nozzle

Nozzle

Overview


A nozzle is a device designed to control the direction or characteristics of a fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

 flow (especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe
Pipe (material)
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases , slurries, powders, masses of small solids...

 via an orifice
Orifice
An orifice is any opening, mouth, hole or vent, as of a pipe, plate, or a body.* Body orifice* Orifice plate* Calibrated orifice* Nozzle* Back Orifice-See also:* Choked flow* Needle valve* Venturi effect* Flow measurement...

.

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
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 or gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

). 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.

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.
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Encyclopedia


A nozzle is a device designed to control the direction or characteristics of a fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

 flow (especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe
Pipe (material)
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases , slurries, powders, masses of small solids...

 via an orifice
Orifice
An orifice is any opening, mouth, hole or vent, as of a pipe, plate, or a body.* Body orifice* Orifice plate* Calibrated orifice* Nozzle* Back Orifice-See also:* Choked flow* Needle valve* Venturi effect* Flow measurement...

.

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
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 or gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

). 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.

Jet


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 stove
Gas stove
In cooking, a gas stove is a cooker which uses natural gas, propane, butane, liquefied petroleum gas or other flammable gas as a fuel source.-History:...

s, oven
Oven
An oven is a thermally insulated chamber used for the heating, baking or drying of a substance. It is most commonly used for cooking. Kilns, and furnaces are special-purpose ovens...

s, or barbecue
Barbecue
Barbecue or barbeque , used chiefly in the United States, Canada, the United Kingdom, New Zealand and Australia is a method and apparatus for cooking meat, poultry and occasionally fish with the heat and hot smoke of a fire, smoking wood, or hot coals of...

s. Gas jets were commonly used for light before the development of electric light
Electric light
Electric lights are a convenient and economic form of artificial lighting which provide increased comfort, safety and efficiency. Most electric lighting is powered by centrally-generated electric power, but lighting may also be powered by mobile or standby electric generators or battery systems...

. Other types of fluid jets are found in carburetor
Carburetor
A carburetor , carburettor, or carburetter is a device that blends air and fuel for an internal combustion engine. It is sometimes shortened to carb in North America and the United Kingdom....

s, where smooth calibrated orifice
Calibrated orifice
A calibrated orifice is a restriction that is deliberately placed into a system of pipes to set the flow rate through the system. The orifice may be designed to produce proportional flow , or choked flow A calibrated orifice is a restriction that is deliberately placed into a system of pipes to...

s are used to regulate the flow of fuel
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

 into an engine, and in jacuzzi
Jacuzzi
Jacuzzi is a company that produces whirlpool bathtubs and spas. Its first product was a bath with massaging jets. The term "jacuzzi" is now often used generically to refer to any bathtub with massaging jets.-History:...

s or spa
Spa
The term spa is associated with water treatment which is also known as balneotherapy. Spa towns or spa resorts typically offer various health treatments. The belief in the curative powers of mineral waters goes back to prehistoric times. Such practices have been popular worldwide, but are...

s.

Another specialized jet is the laminar jet. This is a water jet that contains devices to smooth out the pressure and flow, and gives laminar flow
Laminar flow
Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross currents...

, as its name suggests. This gives better results for fountain
Fountain
A fountain is a piece of architecture which pours water into a basin or jets it into the air either to supply drinking water or for decorative or dramatic effect....

s.

Nozzles used for feeding hot blast
Hot blast
Hot blast refers to the preheating of air blown into a blast furnace or other metallurgical process. This has the result of considerably reducing the fuel consumed in the process...

 into a blast furnace
Blast furnace
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore and flux are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions...

 or forge
Forge
A forge is a hearth used for forging. The term "forge" can also refer to the workplace of a smith or a blacksmith, although the term smithy is then more commonly used.The basic smithy contains a forge, also known as a hearth, for heating metals...

 are called tuyere
Tuyere
A tuyere, also can be spelled as tuyère, is a tube, nozzle or pipe through which air is blown into a furnace or hearth.Air or oxygen is injected into a hearth under pressure from bellows or a blast engine or other devices...

s.

High velocity


Frequently the goal is to increase the kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...

 of the flowing medium at the expense of its pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 and internal energy
Internal energy
In thermodynamics, the internal energy is the total energy contained by a thermodynamic system. It is the energy needed to create the system, but excludes the energy to displace the system's surroundings, any energy associated with a move as a whole, or due to external force fields. Internal...

.

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
De Laval nozzle
A de Laval nozzle is a tube that is pinched in the middle, making a carefully balanced, asymmetric hourglass-shape...

 has a convergent section followed by a divergent section and is often called a convergent-divergent nozzle ("con-di nozzle").

Convergent nozzles accelerate subsonic fluids. If the nozzle pressure ratio is high enough the flow will reach sonic velocity at the narrowest point (i.e. the nozzle throat). In this situation, the nozzle is said to be choked.

Increasing the nozzle pressure ratio further will not increase the throat Mach number
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

 beyond unity. Downstream (i.e. 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
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....

 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
Hypersonic
In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...

 flows are required, and where propellant mixtures are deliberately chosen to further increase the sonic speed.

Divergent nozzles slow fluids, if the flow is subsonic, but accelerate sonic or supersonic fluids.

Convergent-divergent nozzles
De Laval nozzle
A de Laval nozzle is a tube that is pinched in the middle, making a carefully balanced, asymmetric hourglass-shape...

 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 would not contribute to thrust.

Propelling



A jet exhaust produces a net thrust from the energy obtained from combusting fuel which is added to the inducted air. This hot air is passed through a high speed nozzle, a propelling nozzle which enormously increases its kinetic energy.

For a given mass flow, greater thrust is obtained with a higher exhaust velocity, but the best energy efficiency is obtained when the exhaust speed is well matched with the airspeed. However, no jet aircraft can maintain velocity while exceeding its exhaust jet speed, due to momentum considerations. Supersonic jet engines, like those employed in fighter
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...

s and SST
Supersonic transport
A supersonic transport is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. The only SSTs to see regular service to date have been Concorde and the Tupolev Tu-144. The last passenger flight of the Tu-144 was in June 1978 with its last ever...

 aircraft (e.g. Concorde
Concorde
Aérospatiale-BAC Concorde was a turbojet-powered supersonic passenger airliner, a supersonic transport . It was a product of an Anglo-French government treaty, combining the manufacturing efforts of Aérospatiale and the British Aircraft Corporation...

), need high exhaust speeds. 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 employ simple convergent nozzles. In addition, bypass
Bypass ratio
The term bypass ratio relates to the design of turbofan engines, commonly used in aviation. It is defined as the ratio between the mass flow rate of air drawn in by the fan bypassing the engine core to the mass flow rate passing through the engine core....

 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 very high exhaust speeds are desirable.

Magnetic


Magnetic nozzles have also been proposed for some types of propulsion, such as VASIMR, in which the flow of plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 is directed by magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

s instead of walls made of solid matter.

Spray



Many nozzles produce a very fine spray of liquids.
  • Atomizer nozzle
    Atomizer nozzle
    An atomizer nozzle is an aspirator nozzle for producing a fine spray of a liquid based on the Venturi effect.-Principle of operation :When a gas is injected under pressure through a tube with a decreasing section, it speeds up, generating a pressure drop at the narrowest point .The reduced...

    s
    are used for spray painting, perfumes, carburettors for internal combustion engine
    Internal combustion engine
    The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

    s, spray on deodorant
    Deodorant
    Deodorants are substances applied to the body to affect body odor caused by bacterial growth and the smell associated with bacterial breakdown of perspiration in armpits, feet and other areas of the body. A subgroup of deodorants, antiperspirants, affect odor as well as prevent sweating by...

    s, antiperspirants and many other uses.
  • 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.

Shaping


Some nozzles are shaped to produce a stream that is 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. This nozzle is typically referred to as a die
Die (manufacturing)
A die is a specialized tool used in manufacturing industries to cut or shape material using a press. Like molds, dies are generally customized to the item they are used to create...

.

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