Nozzle (redirected from Nozzles)

An orifice in an inkjet print head through which ink is sprayed onto the paper. Print heads with six thousand or more nozzles are common in today's printers.

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Nozzle

A conduit with a variable cross-sectional area in which a fluid accelerates into a high-velocity stream.

The fluid must be compressed to a state of high pressure before it is sent through the nozzle. If the fluid is a gaseous medium, the temperature of the fluid also drops as the fluid accelerates. Since the velocity of sound of the fluid is directly related to the temperature of the fluid, the fluid velocity may exceed the speed of sound of the fluid, so that the fluid is in a state of supersonic flow. Under this condition, the nozzle must have a convergent-divergent geometry, since the supersonic state is realized only in the divergent portion of the nozzle (see illustration). The Mach number, which is the ratio of the velocity of the flowing fluid to the velocity of sound of the fluid, may be employed to characterize the flow. The Mach number is less than unity if the flow is subsonic, unity if the flow is sonic, and larger than unity if the flow is supersonic. If the flow at the throat is sonic, the flow is said to reach the critical state.

A nozzle can be used for a variety of purposes. It is an indispensable piece of equipment in many devices employing fluid as a working medium. The reaction force that results from the fluid acceleration may be employed to propel a jet aircraft or a rocket. In fact, most military jet aircraft employ the simple convergent conical nozzle, with adjustable conical angle, as their propulsive device. If the high-velocity fluid stream is directed to turn a turbine, it may generate electric power or drive an automotive vehicle. The high-velocity stream may also be produced inside a wind tunnel so that the conditions of flight of a missile or an aircraft may be simulated inside the tunnel for research purposes. The nozzle must be carefully designed in this case to provide uniformly flowing fluid with the desired velocity, pressure, and temperature at the test section of the wind tunnel. Nozzles may also be used to disperse fuel into an atomized mist, such as that in diesel engines, for combustion purposes. See Atomization, Impulse turbine, Internal combustion engine, Jet propulsion, Rocket propulsion, Wind tunnel