[Edit]

The Venturi effect is a special case of Bernoulli's principle, in the case of fluid or air flow through a tube or pipe with a constriction in it. The fluid must speed up in the restriction, reducing its pressure and producing a partial vacuum via the Bernoulli effect. It is named after Giovanni Battista Venturi, (1746–1822), an Italian physicist. A fluid passing through smoothly varying constrictions is subject to changes in velocity and pressure in order to satisfy the conservation of mass-flux (flow rate). The reduction in pressure in the constriction can be understood by conservation of energy: the fluid (or gas) gains kinetic energy as it enters the constriction, and that energy is supplied by a pressure gradient force from behind. The pressure gradient reduces the pressure in the constriction, in reaction to the acceleration. Likewise, as the fluid leaves the constriction, it is slowed by a pressure gradient force that raises the pressure back to the ambient level. The limiting case of the Venturi effect is choked flow, in which a constriction in a pipe or channel limits the total flow rate through the channel, because the pressure cannot drop below zero in the constriction. Choked flow is used to control the delivery rate of water and other fluids through spigots and other valves.

top

Venturi Tubes

The simplest apparatus, as shown in the photograph and diagram, is a tubular setup known as a Venturi tube or simply a venturi. Fluid flows through a length of pipe of varying diameter. To avoid undue drag, a venturi tube typically has an entry cone of 30 degrees and an exit cone of 5 degrees.

A venturi can also be used to mix a fluid with air. If a pump forces the fluid through a tube connected to a system consisting of a venturi to increase the water speed (the diameter decreases), a short piece of tube with a small hole in it, and last a venturi that decreases speed (so the pipe gets wider again), air will be sucked in through the small hole because of changes in pressure. At the end of the system, a mixture of fluid and air will appear.

Orifice plate

Venturi tubes are more expensive to construct than a simple orifice plate which uses the same principle as a tubular scheme, but the orifice plate causes significantly more permanent energy loss and is less accurate.

top

the capillaries of the human circulatory system, where it indicates aortic regurgitation

large cities where wind is forced between buildings.

gas jets that mix air and flammable gas in barbecues, gas stoves, and Bunsen burners

water aspirators that produce partial vacuum from a water spigot

atomizers that disperse perfume

foam firefighting nozzles and extinguishers

carburetors that use the effect to suck gasoline into an engine's intake air stream.

Buchner funnels that use the Venturi effect to provide the suction on force against the contents of the funnel

Protein skimmers, a filtration device for saltwater aquaria.

in automated swimming pool cleaning robots that use pressure-side water flow to collect sediment and debris.

the modern day barrel of the Clarinet, which uses a reverse taper to speed the air down the tube, enabling better tone, response and intonation.

top

Bernoulli's principle

Choked flow

Orifice plate

Bunsen burner