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[[File:Quat.JPG|thumb|right|A typical electric fan]]
[[File:Small Desk Fan 1.jpg|thumb|A table fan]]
[[File:N7771@GVA;09.09.1995-engine (6083468531).jpg|thumb|alt=Crowd of people standing around a large engine of a Boeing 777|Fans are used to force air into [[Turbofan|low- and high
A '''fan''' is a powered machine used to create a flow of air. A fan consists of a rotating arrangement of vanes or blades, generally made of wood, plastic, or metal, which act on the air. The rotating assembly of blades and hub is known as an ''[[impeller]]'', ''[[Rotor (electric)|rotor]]'', or ''runner''. Usually, it is contained within some form of housing, or case.<ref>{{cite encyclopedia |url=https://www.britannica.com/EBchecked/topic/201417/fan |title=Fan |encyclopedia=Encyclopædia Britannica |access-date=2012-05-19}}</ref> This may direct the airflow, or increase safety by preventing objects from contacting the fan blades. Most fans are powered by [[electric motor]]s, but other sources of power may be used, including [[hydraulic motor]]s, [[handcrank]]s, and [[internal combustion engine]]s.
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In [[South Korea]], fans play a part in an [[Old wives' tale|old wives tale]]. Many older South Korean citizens believe in the unscientific and unsupported myth of [[fan death]] due to excessive use of an electric fan; Korean electric fans usually turn off after a few hours to protect from fan death.
== Types ==
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{{More citations needed section|find=year when Key contributions were made by Coester, Ilberg and Sadeh, Porter and Markland, and Eck.|date=November 2023}}
The ''cross-flow'' or ''tangential'' fan, sometimes known as a ''tubular'' fan, was patented in 1893 by Paul Mortier,<ref>Paul Mortier. ''Fan or Blowing apparatus''. [https://
The flow within a cross-flow fan may be broken up into three distinct regions: a vortex region near the fan discharge, called an eccentric vortex, the through-flow region, and a paddling region directly opposite. Both the vortex and paddling regions are dissipative, and as a result, only a portion of the impeller imparts usable work on the flow.<ref>{{Cite journal |last1=Porter |first1=A. M. |last2=Markland |first2=E. |date=December 1970 |title=A Study of the Cross Flow Fan |url=http://journals.sagepub.com/doi/10.1243/JMES_JOUR_1970_012_071_02 |journal=Journal of Mechanical Engineering Science |language=en |volume=12 |issue=6 |pages=421–431 |doi=10.1243/JMES_JOUR_1970_012_071_02 |issn=0022-2542}}</ref> The cross-flow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the crossflow fan in HVAC comes from its compactness, shape, quiet operation, and ability to provide a high pressure coefficient. Effectively a rectangular fan in terms of inlet and outlet geometry, the diameter readily scales to fit the available space, and the length is adjustable to meet flow rate requirements for the particular application.
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Since the flow both enters and exits the impeller radially, the crossflow fan has been studied and prototyped for potential aircraft applications.<ref>{{Cite journal |last1=Himeur |first1=Rania M. |last2=Khelladi |first2=Sofiane |last3=Ait Chikh |first3=Mohamed Abdessamed |last4=Vanaei |first4=Hamid Reza |last5=Belaidi |first5=Idir |last6=Bakir |first6=Farid |date=January 2022 |title=Towards an Accurate Aerodynamic Performance Analysis Methodology of Cross-Flow Fans |journal=Energies |language=en |volume=15 |issue=14 |pages=5134 |doi=10.3390/en15145134 |issn=1996-1073 |doi-access=free }}</ref> Due to the two-dimensional nature of the flow, the fan can be integrated into a wing for use in both thrust production and boundary-layer control. A configuration that utilizes a crossflow fan is located at the wing [[leading edge]] is the [[FanWing]] design concept initially developed around 1997 and under development by a company of the same name. This design creates lift by deflecting the wake downward due to the rotational direction of the fan, causing a large [[Magnus effect|Magnus force]], similar to a spinning leading-edge cylinder. Another configuration utilizing a crossflow fan for thrust and flow control is the [[propulsive wing]], another experimental concept prototype initially developed in the 1990s and 2000s. In this design, the crossflow fan is placed near the [[trailing edge]] of a thick wing and draws the air of the wing's suction (top) surface. By doing this, the propulsive wing is nearly stall-free, even at extremely high angles of attack, producing very high lift. However, the fanwing and propulsive wing concepts remain experimental and have only been used for unmanned prototypes.
A cross-flow fan is a centrifugal fan in which the air flows straight through the fan instead of at a right angle. The rotor of a cross-flow fan is covered to create a pressure differential.
=== Bladeless fans ===
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===Jet fan===
In ventilation systems a jet fan, also known as an impulse or induction fan, ejects a stream of air which entrains ambient air along with it, in order to circulate the ambient air. The system takes up less space than conventional ventilation ducting and can significantly increase the rates of inflow of fresh air and expulsion of stale air.<ref>[https://www.systemair.com/fileadmin/user_upload/systemair-b2b/Local/Czech_Republic/Catalogues/02_Fans_Accessories/jet-fan-systems_2017-02_en_e1749.pdf Jet Fan Systems] {{Webarchive|url=https://web.archive.org/web/20220224005341/https://www.systemair.com/fileadmin/user_upload/systemair-b2b/Local/Czech_Republic/Catalogues/02_Fans_Accessories/jet-fan-systems_2017-02_en_e1749.pdf |date=2022-02-24 }}, Syetemair, 2017. (retrieved 22 March 2022)</ref>
== Noise ==
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== Fan motor drive methods ==
[[File:UMA 2.JPG|thumb|Building heating and cooling systems commonly use
Standalone fans are usually powered by an [[electric motor]], often attached directly to the motor's output, with no gears or belts. The motor is either hidden in the fan's center hub or extends behind it. For big industrial fans, three-phase asynchronous motors are commonly used, may be placed near the fan, and drive it through a [[Pulley#Belt and pulley systems|belt and pulleys]]. Smaller fans are often powered by [[Shaded-pole motor|shaded pole AC motors]], or [[Brushed DC Electric Motor|brushed]] or [[Brushless DC electric motor|brushless DC motors]]. AC-powered fans usually use mains voltage, while DC-powered fans typically use low voltage, typically 24V, 12V, or 5 V.
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In machines with a rotating part, the fan is often connected to it rather than being powered separately. This is commonly seen in motor vehicles with [[internal combustion engine]]s, large cooling systems, locomotives, and winnowing machines, where the fan is connected to the [[drive shaft]] or through a belt and pulleys. Another common configuration is a dual-shaft motor, where one end of the shaft drives a mechanism, while the other has a fan mounted on it to cool the motor itself. Window [[air conditioner]]s commonly use a dual-shaft fan to operate separate fans for the interior and exterior parts of the device.
Where electrical power or rotating parts are not readily available, fans may be driven by other methods. High-pressure gases such as steam can be used to drive a small [[turbine]], and high-pressure liquids can be used to drive a [[pelton wheel]], either of which can provide the rotational drive for a fan.
Large, slow-moving energy sources such as a flowing river can also power a fan using a [[water wheel]] and a series of step-down gears or pulleys to increase the rotational speed to that which is required for efficient fan operation.
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=== Solar power ===
Electric fans used for ventilation may be powered by [[Photovoltaic module|solar panels]] instead of mains current. This is an attractive option because once the capital costs of the solar panel have been covered, the resulting electricity is free.
A typical example uses a detached 10-[[watt]], {{convert|12|×|12|in|cm|adj=on|abbr=on}} solar panel and is supplied with appropriate brackets, [[Power cable|cables]], and [[Electrical connector|connectors]]. It can be used to ventilate up to {{convert|1250|sqft}} of [[area]] and can move air at up to {{convert|800|cuft/min|L/s|-2}}. Because of the wide availability of 12 V [[brushless DC electric motor]]s and the convenience of wiring such a low voltage, such fans usually operate on 12 [[volt]]s.
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