Nozzle

 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.

Types

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.

High velocity

A de Laval nozzle has a convergent section followed by a divergent section and is often called a convergent-divergent nozzle .
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 increase 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.

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.
They thus 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.

Spray

Air-Aspirating Nozzle-uses an opening in the cone shaped nozzle to inject air into a stream of water based foam to make the concentrate "foam up".