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jet nozzle[′jet ¦näz·əl]
a contoured nozzle, such as an outlet or the blade passage of a guide-vane assembly, installed in pipelines or enclosed conduits in order to convert the potential energy of a flowing working fluid, such as a liquid, steam, or gas, into kinetic energy. After the working fluid passes through the nozzle, its velocity is increased.
The first such nozzle was used by C. G. P. de Laval in 1889 to increase the velocity of steam ahead of the rotor in a steam turbine. The theory of the jet nozzle was developed by S. A. Chaplygin in 1902. Convergent nozzles are used to create subsonic flow velocities (seeMACH NUMBER), and nozzles with an expanding outlet portion (Laval nozzles) are used to obtain supersonic velocities. Jet nozzles are employed in hydraulic, steam, and gas turbines and in jet engines; they are also used in measurement technology, as in venturi tubes and flowmeters.