Nozzle

A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) 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.

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.

Jet nozzles are also used in large rooms where the distribution of air via ceiling diffusers is not possible or not practical.

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.

Convergent-divergent nozzles can therefore accelerate fluids that have choked in the convergent section to supersonic speeds.

Jet engines for subsonic flight use convergent nozzles with a sonic exit velocity.