{{Short description|Machine used to produce air flow}} {{About|mechanical fans|hand-powered fans|Hand fan|other uses|Fan (disambiguation)}} [[File:Hatari 18 inch fan.jpg|thumb|upright|A household electric fan]]
A '''fan''' is a powered machine that creates airflow. A fan consists of rotating 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 housing will allow air to past through as well as directing the airflow, or increasing 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.
Mechanically, a fan can be any revolving [[wikt:vane#English|vane]], or vanes used for producing [[Air current|currents of air]]. Fans produce air flows with high [[volume]] and low [[pressure]] (although higher than [[ambient pressure]]), as opposed to [[gas compressor|compressors]] which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air-fluid stream, and devices that take advantage of this, such as [[anemometer]]s and [[wind turbine]]s, often have designs similar to that of a fan.
Typical applications include [[HVAC#Ventilation|climate control]] and personal [[thermal comfort]] (e.g., an electric table or floor fan), vehicle engine cooling systems (e.g., in front of a radiator), machinery cooling systems (e.g., inside computers and [[audio power amplifier]]s), ventilation, fume extraction, [[winnowing]] (e.g., separating [[chaff]] from [[cereal]] grains), removing dust (e.g. sucking as in a vacuum cleaner), drying (usually in combination with a heat source) and providing draft for a fire. Some fans may be indirectly used for cooling in the case of industrial heat exchangers.
While fans are effective at cooling people, they do not cool air. Instead, they work by [[evaporative cooling]] of [[sweat]] and increased heat [[convection]] into the surrounding air due to the airflow from the fans. Thus, fans may become less effective at cooling the body if the surrounding air is near body temperature and contains high humidity.
== History == [[File:Patent, Mechanical Fan, 1830.png|thumb|[[Patent drawing]] for a ''Fan Moved by Mechanism'', invented by James Barron, November 27, 1830]]
Fans made with leaves were prevalent in ancient Egypt and India.<ref>{{Cite web |date=2016-08-10 |title=The Past and Present of the Fan |url=https://www.archaeology.wiki/blog/2016/08/10/past-present-fan/ |website=Archaeology Wiki |access-date=2025-11-20 }}</ref><ref>{{Cite web |title=Fans in Antiquity – The Fan Circle |url=https://fancircleinternational.org/fans-in-antiquity/ |access-date=2025-11-20 }}</ref> In ancient India, they were handheld fans made from bamboo strips or other plant fiber, that could be rotated or fanned to move air. During [[British India|British rule]], the word came to be used by Anglo-Indians to mean a large swinging flat fan, fixed to the ceiling and pulled by a servant called the [[punkawallah]].
For purposes of [[air conditioning]], the [[Han dynasty]] craftsman and engineer [[Ding Huan]] (fl. 180 CE) invented a manually operated rotary fan with seven wheels that measured 3 m (10 ft) in diameter; in the 8th century, during the [[Tang dynasty]] (618–907), the Chinese applied [[Hydraulics|hydraulic power]] to rotate the fan wheels for air conditioning, while the rotary fan became even more common during the [[Song dynasty]] (960–1279).<ref>Needham (1986), Volume 4, Part 2, 99, 134, 151, 233.</ref><ref>Day & McNeil (1996), 210.</ref>
During the [[Heian period|Heian]] period (794–1185) in Japan, fans adapted the role of symbolizing social class as well as a mechanical role. The [[tessen]], a Japanese fan used in [[Feudalism|Feudal]] times, was a dangerous weapon hidden in plain sight in the shape of a regular fan, a weapon used by [[samurai]]s when [[katana]]s were not ideal.
In the 17th century, the experiments of scientists, including [[Otto von Guericke]], [[Robert Hooke]], and [[Robert Boyle]], established the basic principles of vacuum and airflow. The English architect Sir [[Christopher Wren]] applied an early ventilation system in the [[Houses of Parliament]] that used bellows to circulate air. Wren's design was the catalyst for much later improvement and innovation. The first rotary fan used in Europe was for mine ventilation during the 16th century, as illustrated by [[Georg Agricola]] (1494–1555).<ref>Needham, Volume 4, Part 2, 154.</ref>
[[John Theophilus Desaguliers]], a British engineer, demonstrated the successful use of a fan system to draw out stagnant air from coal mines in 1727—ventilation was essential in coal mines to prevent asphyxiation—and soon afterward he installed a similar apparatus in Parliament.<ref>{{cite web |url=http://www.fanmakers.com/text.aspx?id=26 |title=A Short History of Mechanical Fans |publisher=The Worshipful Company of Fan Makers |archive-url=https://web.archive.org/web/20131204080959/http://www.fanmakers.com/text.aspx?id=26 |archive-date=December 4, 2013 }}</ref> The civil engineer [[John Smeaton]], and later [[John Buddle]], installed reciprocating air [[pump]]s in the mines in the North of England, though the machinery was liable to breaking down.
=== Steam === In 1849 a 6m radius steam-driven fan, designed by [[William Brunton]], was made operational in the Gelly Gaer [[Colliery]] of [[South Wales]]. The model was exhibited at the [[Great Exhibition]] of 1851. Also in 1851 [[David Boswell Reid]], a Scottish doctor installed four steam-powered fans in the ceiling of [[St George's Hospital]] in [[Liverpool]] so that the pressure produced by the fans would force the incoming air upward and through vents in the ceiling.<ref>{{cite web |last=Bruegmann |first=Robert |title=Central Heating and Ventilation:Origins and Effects on Architectural Design |url=http://isites.harvard.edu/fs/docs/icb.topic753413.files/8_Engineers%20Contractors%20and%20Industrial%20Construction/Bruegmann_Central.pdf |archive-url=https://web.archive.org/web/20160121152758/http://isites.harvard.edu/fs/docs/icb.topic753413.files/8_Engineers%20Contractors%20and%20Industrial%20Construction/Bruegmann_Central.pdf |archive-date=January 21, 2016 }}</ref><ref>{{cite web |last=Roberts |first=Brian |title=Historic Building Engineering Systems & Equipment Heating & Ventilation |url=https://content.historicengland.org.uk/images-books/publications/heating-ventilation/heatingventilation.pdf/ |archive-url=https://web.archive.org/web/20161101102149/https://content.historicengland.org.uk/images-books/publications/heating-ventilation/heatingventilation.pdf/ |archive-date=2016-11-01 |format=PDF |publisher=CIBSE Heritage Group }}</ref> Improvements in the technology were made by [[James Nasmyth]], Frenchman Theophile Guibal and J. R. Waddle.<ref>{{cite book |last=Cory |first=William |date=2010 |url=https://books.google.com/books?id=x-pL19ro-qsC |title=Fans and Ventilation: A Practical Guide |publisher=Elsevier |isbn=978-0-08-053158-8 }}</ref>
=== Electrical === [[File:Elektrische ventilator van het merk Calor - INDUS V09832.JPG|thumb|Electric fan in [[Bakelite]], collection of the Museum of Industry (Ghent, Belgium)]]
Between 1882 and 1886 [[Schuyler Wheeler]] invented a fan powered by electricity.<ref>{{cite web |title=B. A. C. (Before Air Conditioning) |url=http://www.neworleansbar.org/documents/BeforeA.C.8-5_000.pdf |archive-url=https://web.archive.org/web/20120903102224/http://www.neworleansbar.org/documents/BeforeA.C.8-5_000.pdf |archive-date=2012-09-03 |publisher=New Orleans Bar Association }}</ref> It was commercially marketed by the American firm Crocker & Curtis electric motor company. In 1885 a desktop direct drive electric fan was commercially available by Stout, Meadowcraft & Co. in New York.<ref>{{cite magazine |date=1885-07-18 |title=Electric Fan |url=https://books.google.com/books?id=J4U9AQAAIAAJ |magazine=[[Scientific American]] |publisher=Munn & Company |page=37 }}</ref>
In 1882, [[Philip Diehl (inventor)|Philip Diehl]] developed the world's first electric [[Ceiling fan|ceiling mounted fan]]. During this intense period of innovation, fans powered by alcohol, oil, or kerosene were common around the turn of the 20th century.
In 1909, [[KDK]] of Japan pioneered the invention of mass-produced electric fans for home use. In the 1920s, industrial advances allowed steel fans to be mass-produced in different shapes, bringing fan prices down and allowing more homeowners to afford them. In the 1930s, the first art deco fan (the "Silver Swan") was designed by Emerson.<ref>{{cite web |date=2023 |url=https://mohistory.org/museum/50-objects/emerson-silver-swan-fan |title=Emerson Silver Swan Fan |website=MoHistory.org |publisher=Missouri Historical Society |access-date=2026-04-30 }}</ref> By the 1940s, [[Crompton Greaves]] of India became the world's largest manufacturer of electric ceiling fans mainly for sale in India, Asia, and the Middle East. By the 1950s, table and stand fans were manufactured in bright colors and were eye-catching. Ceiling fans are extremely popular in South Asian countries such as India, where they provide cost-effective cooling in hot climates.<ref>{{cite news |date=10 June 2022 |title=Indian Fans Market Warming Up to BLDC |url=https://www.thehindubusinessline.com/specials/india-interior/indian-fans-market-warming-up-to-bldc/article65506366.ece |work=The Hindu BusinessLine |access-date=5 July 2025 }}</ref><ref>{{cite news |title=A majority of Indian homes still depend on ceiling fans for cooling |url=https://www.livemint.com/industry/manufacturing/ceiling-fans-remain-indian-households-top-cooling-choice-despite-rise-of-air-conditioners-11688483901249.html |work=Livemint |date=14 July 2023 |access-date=5 July 2025 }}</ref>
Window and central [[air conditioning]] in the 1960s caused many companies to discontinue production of fans,<ref>{{cite web |last=Cunningham |first=Steve |title=A Brief History of Fans |url=http://www.fancollectors.org/fanhistory.htm |website=Fancollectors.org |publisher=Antique Fan Collectors Association |access-date=July 5, 2010 }}</ref> but in the mid-1970s, with an increasing awareness of the cost of electricity and the amount of energy used to heat and cool homes, turn-of-the-century styled ceiling fans became popular again as both decorative and energy-efficient.
In 1998 William Fairbank and Walter K. Boyd invented the [[High-volume low-speed fan|high-volume low-speed (HVLS) ceiling fan]], designed to reduce energy consumption by using long fan blades rotating at low speed to move a relatively large volume of air.<ref>{{cite web |last=Greenfield |first=David |date=December 20, 2010 |title=Industrial Fan Designer Finds Niche in Energy Efficiency – Automation and Control |url=http://www.designnews.com/blog/Automation_and_Control/40243-Industrial_Fan_Designer_Finds_Niche_in_Energy_Efficiency.php |archive-url=https://web.archive.org/web/20101227180929/http://www.designnews.com/blog/Automation_and_Control/40243-Industrial_Fan_Designer_Finds_Niche_in_Energy_Efficiency.php |archive-date=2010-12-27 |work=[[Design News]] |publisher=[[Informa]] |access-date=May 18, 2011 }}</ref>
== Types == [[File:Ceiling fan with lamp.jpg|thumb|Ceiling fan with an [[electric light]]]]
Mechanical revolving blade fans are made in a wide range of designs. They are used on the floor, table, desk, or hung from the ceiling ([[ceiling fan]]) and can be built into a window, wall, roof, etc. Tower fans tend to have smaller blades inside. Electronic systems generating significant heat, such as [[computer]]s, incorporate fans. Appliances such as hair dryers and space heaters also use fans. They move air in air-conditioning systems and in automotive engines. Fans used for comfort inside a room create a [[wind chill]] by increasing the [[heat transfer coefficient]] but do not lower temperatures directly. Fans used to cool electrical equipment or in engines or other machines cool the equipment directly by exhausting hot air into the cooler environment outside of the machine so that cooler air flows in. Three main types of fans are used for moving air, ''axial'', ''centrifugal'' (also called ''radial'') and ''cross flow'' (also called ''tangential''). The [[American Society of Mechanical Engineers]] (ASME) Performance Testing Code (PTC) 11 provides standard procedures for conducting and reporting tests on fans, including those of the centrifugal, axial, and mixed flows.<ref>{{cite tech report |url=https://www.asme.org/codes-standards/publications-information/performance-test-codes |publisher=ASME |id=PTC 11 |title=Fans |access-date=2026-03-05 }}</ref>
=== Axial-flow === {{More citations needed section|date=May 2026}} [[File:Luefter y.s.tech pd1270153b-2f.jpg|thumb|An axial box fan for cooling electrical equipment]]
Axial-flow fans have blades that force air to move [[Parallel (geometry)|parallel]] to the shaft about which the blades rotate. This type of fan is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in [[cooling tower]]s. Axial flow fans are applied in air conditioning and industrial process applications. Standard axial flow fans have diameters of 300–400 mm or 1,800–2,000 mm and work under pressures up to 800 [[Pascal (unit)|Pa]]. Special types of fans are used as low-pressure compressor stages in aircraft engines. Examples of axial fans are: * Table fan: Basic elements of a typical table fan include the fan blade, base, armature, and lead [[wire]]s, motor, blade [[safety barrier|guard]], motor housing, [[oscillator]] gearbox, and oscillator shaft. The oscillator is a mechanism that motions the fan from side to side. The armature axle shaft comes out on both ends of the motor; one end of the shaft is attached to the blade, and the other is attached to the oscillator gearbox. The motor case joins the gearbox to contain the rotor and stator. The oscillator shaft combines the weighted base and the gearbox. A motor housing covers the oscillator mechanism. The blade guard joins the motor case for safety. * Domestic extractor fan: Wall- or ceiling-mounted, the domestic extractor fan is employed to remove moisture and stale air from domestic dwellings. Bathroom extractor fans typically utilize a four-inch (100 mm) impeller, while kitchen extractor fans typically use a six-inch (150 mm) impeller as the room is often bigger. Axial fans with five-inch (125 mm) impellers are also used in larger bathrooms, though they are much less common. Domestic axial extractor fans are unsuitable for duct runs over 3 m or 4 m, depending on the number of bends in the run, as the increased air pressure in longer pipework inhibits the fan's performance. * Continuous running extractor fans run continuously at a very slow rate, running fast when necessary, for example when a bathroom light is switched on. At working speed, they are just normal extractor fans. They extract typically 5 to 10 l/sec at continuous speed and use little electricity, 1 or 2 watts, for low annual cost. Some have humidity sensors to control trickle operation. They have the advantage of ensuring ventilation and preventing the build-up of humidity. Alternatively, a normal extractor fan may be fitted to operate intermittently at full power for the same purpose.<ref>{{cite web |last=MacEachern |first=Ruth |date=24 October 2022 |title=Do extractor fans cost a lot to run? |url=https://www.envirovent.com/blog/do-extractor-fans-cost-a-lot-to-run/ |publisher=EnviroVent |access-date=}}</ref> * Electro-mechanical fans: Among collectors, are rated according to their condition, size, age, and number of blades. Four-blade designs are the most common. Five-blade or six-blade designs are rare. The materials from which the components are made, such as brass, are important factors in fan desirability. * A ceiling fan is a fan suspended from the ceiling of a room. Most ceiling fans rotate at relatively low speeds and do not have blade guards because they are inaccessible and unwieldy. Ceiling fans are used in both residential and industrial/commercial settings. * In [[automobile]]s, a mechanical or electrically driven fan provides [[engine cooling]] and prevents the engine from overheating by blowing or drawing air through a [[coolant]]-filled [[radiator]]. The fan may be driven with a [[Pulley#Belt and pulley systems|belt and pulley]] off the [[Internal-combustion engine|engine]]'s [[crankshaft]] or an electric motor switched on or off by a [[thermostat]]ic [[switch]]. * [[Computer fan]] for cooling electrical components and in [[laptop cooler]]s. * Fans inside [[audio power amplifier]]s help to draw heat away from the electrical components. * [[Variable pitch fan]]: A variable-pitch fan is used to precisely control static pressure within supply ducts. The blades are arranged to rotate upon a control-pitch hub. The fan wheel will spin at a constant speed. The blades follow the control pitch hub. As the hub moves toward the rotor, the blades increase their angle of attack, and an increase in flow results.
=== Centrifugal === {{Main|Centrifugal fan}}
Often called a "squirrel cage" (because of its general similarity in appearance to [[Hamster wheel|exercise wheels]] for pet rodents) or "scroll fan", the centrifugal fan has a moving component (called an ''[[impeller]]'') that consists of a central shaft about which a set of blades that form a [[spiral]], or ribs, are positioned. Centrifugal fans blow air at right angles to the intake of the fan and spin the air outwards to the outlet (by deflection and [[centrifugal force]]). The impeller rotates, causing air to enter the fan near the shaft and move [[perpendicular]]ly from the shaft to the opening in the scroll-shaped fan casing. A centrifugal fan produces more pressure for a given air volume, and is used where this is desirable such as in [[leaf blower]]s, [[blowdryer]]s, air mattress inflators, [[inflatable structure]]s, [[climate control]] in [[Air handler|air handling units]] and various industrial purposes. They are typically noisier than comparable axial fans (although some types of centrifugal fans are quieter such as in air handling units).
<gallery> Centrifugal fan.png|A diagram of a centrifugal fan, with a top view to show airflow CentrifugalFan.png|Typical centrifugal fan Centrifugal Cooling Fan.jpg|Centrifugal cooling fan installed within a laptop. The fan displaces air over the fin stack, which contains a pair of heat pipes. </gallery>
===<span id="Tangential fan"></span> Cross-flow === [[File:Cross-flow fan schematic patent.png|thumb|Cross-section of a cross-flow fan, from the 1893 patent. The rotation is clockwise. The stream guide ''F'' is usually not present in modern implementations.]] [[File:Tangential-flow-coloured-labels.png|thumb|Cross-flow fan]]
The ''cross-flow'' or ''tangential'' fan, sometimes known as a ''tubular'' fan, was patented in 1893 by Lionel Hightower,<ref>Paul Mortier. ''Fan or Blowing apparatus''. [https://patents.google.com/patent/US507445 US Pat. No. 507,445]</ref><ref>{{Cite web |title=Everything You Should Know About Cross Flow Fan - PBM Motor and Fan |url=https://www.pbmmf.com/news/everything-you-should-know-about-cross-flow-fan.html |access-date=2023-11-29 |website=PBM }}</ref> and is used extensively in [[heating, ventilation, and air conditioning]] (HVAC), especially in ductless split air conditioners. The fan is usually long relative to its diameter, so the flow remains approximately two-dimensional away from the ends. The cross-flow fan uses an impeller with forward-curved blades, placed in a housing consisting of a rear wall and a [[vortex]] wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice.
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 |volume=12 |issue=6 |pages=421–431 |doi=10.1243/JMES_JOUR_1970_012_071_02 |issn=0022-2542 |url-access=subscription }}</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.
Common household tower fans are also cross-flow fans.<ref>{{Cite web |title=Tangential Fans: Introduction and Working Principle Discussed |url=https://sofasco.com/blogs/article/tangential-fans-introduction-and-working-principle-discussed |website=Sofasco Fans |access-date=2023-11-29 }}</ref> Much of the early work focused on developing the cross-flow fan for both high- and low-flow-rate conditions and resulted in numerous patents. Key contributions were made by Coester, Ilberg and Sadeh, Porter and Markland, and Eck.{{when|date=July 2022}} One interesting phenomenon particular to the cross-flow fan is that, as the blades rotate, the local air incidence angle changes. The result is that in certain positions, the blades act as compressors (pressure increase), while at other azimuthal locations, the blades act as [[turbine]]s (pressure decrease).
Since the flow 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 |volume=15 |issue=14 |page=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 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 from 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. A cross-flow fan has two walls outside the impeller and a thick vortex wall inside. The radial gap decreases in the direction of the impeller rotation. The rear wall has a log-spiral profile, while the vortex stabilizer is a thin horizontal wall with a rounded edge.<ref>{{Cite journal |last1=Casarsa |first1=L. |last2=Giannattasio |first2=P. |date=September 2011 |title=Experimental study of the three-dimensional flow field in cross-flow fans |url=http://dx.doi.org/10.1016/j.expthermflusci.2011.01.015 |journal=Experimental Thermal and Fluid Science |volume=35 |issue=6 |pages=948–959 |doi=10.1016/j.expthermflusci.2011.01.015 |bibcode=2011ETFS...35..948C |issn=0894-1777 |url-access=subscription }}</ref> The resultant pressure difference allows air to flow straight through the fan, even though the fan blades counter the flow of air on one side of the rotation. Cross-flow fans give airflow along the entire width of the fan; however, they are noisier than ordinary centrifugal fans. Cross-flow fans are often used in ductless [[air conditioner]]s, [[air door]]s, in some types of [[laptop cooler]]s, in automobile ventilation systems, and for cooling in medium-sized equipment such as [[photocopier]]s.<ref>{{Cite book |last=Mitchell |first=John W. |title=Principles of Heating, Ventilation, and Air Conditioning in Buildings |last2=Braun |first2=James E. |publisher=Wiley |date=2013 |isbn=978-0470624579 }}</ref>
=== Bladeless fans === {{Main|Bladeless fan}} [[File:XinHui 新會碧桂園 Country Garden 大潤發 RT-Mart Fresh Food 01.JPG|thumb|An open-face supermarket freezer with an air curtain. Cooling air circulates across the food through the dark slot seen at the rear of the freezer, and through another grille not visible along the front.]]
[[Dyson Air Multiplier]] fans introduced to the consumer market in 2009 have popularized a 1981 design by [[Toshiba]] that produces a fan that has no exposed fan blades or other visibly moving parts (unless augmented by other features such as for oscillation and directional adjustment).<ref name="telegraph.co.uk" /> A relatively small quantity of air from a high-pressure-bladed impeller fan, which is contained inside the base rather than exposed, induces the slower flow of a larger airmass through a circular or oval-shaped opening via a low-pressure area created by an [[airfoil]] surface shape (the [[Coandă effect]]).<ref name="telegraph.co.uk">{{cite news |url=https://www.telegraph.co.uk/technology/news/6377644/Dyson-fan-was-it-invented-30-years-ago.html |archive-url=https://ghostarchive.org/archive/20220112/https://www.telegraph.co.uk/technology/news/6377644/Dyson-fan-was-it-invented-30-years-ago.html |archive-date=2022-01-12 |url-access=subscription |url-status=live |location=London |work=The Daily Telegraph |first=Harry |last=Wallop |title=Dyson fan: was it invented 30 years ago? |date=October 20, 2009}}{{cbignore}}</ref><ref>{{cite web |first=Mark |last=Wilson |date=October 12, 2009 |url=https://gizmodo.com/5379890/dyson-air-multiplier-review-making-a-300-fan-takes-cojones |title=Dyson Air Multiplier Review: Making a $300 Fan Takes Cojones |website=[[Gizmodo]] |access-date=September 9, 2017 |archive-date=September 29, 2018 |archive-url=https://web.archive.org/web/20180929065827/https://gizmodo.com/5379890/dyson-air-multiplier-review-making-a-300-fan-takes-cojones |url-status=dead }}</ref><ref>{{cite web |url=http://www.crunchgear.com/2009/10/12/video-review-the-dyson-air-multiplier/ |title=Video Review: The Dyson Air Multiplier |date=October 12, 2009 |first=John |last=Biggs |website=[[TechCrunch]] |access-date=May 22, 2011 |archive-date=March 15, 2011 |archive-url=https://web.archive.org/web/20110315080558/http://www.crunchgear.com/2009/10/12/video-review-the-dyson-air-multiplier/ |url-status=dead }}</ref>
[[Air door|Air curtains and air doors]] also utilize this effect to help retain warm or cool air within an otherwise exposed area that lacks a cover or door. Air curtains are commonly used on open-face dairy, freezer, and vegetable displays to help retain chilled air within the cabinet using a laminar airflow circulated across the display opening. The airflow is typically generated by a mechanical fan of any type, as described in this article, and is hidden in the base of the display cabinet. [[Heating, ventilation, and air conditioning|HVAC]] linear slot [[Diffuser (thermodynamics)|diffusers]] also utilize this effect to increase airflow evenly in rooms compared to [[Register (air and heating)|registers]] while reducing the energy used by the [[Air handler|air handling unit]] [[Centrifugal fan|blower]].
==Installation== Fans may be installed in various ways, depending on the application. They are often used in free installations without any housing. There are also some specialised installations.
===Ducted fan=== {{Main|Ducted fan}}
In vehicles, a ducted fan is a method of propulsion in which a fan, [[propeller]] or rotor is surrounded by an aerodynamic duct or shroud which enhances its performance to create aerodynamic thrust or lift to transport the vehicle.
===Jet fan=== In ventilation systems, a jet fan, also known as an impulse or induction fan, ejects a stream of air that entrains ambient air 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 == Fans generate noise from the rapid flow of air around blades and obstacles causing vortexes, and from the motor. Fan noise is roughly proportional to the fifth power of fan speed; halving speed reduces noise by about 15 [[Decibel#Acoustics|dB]].<ref>[http://www.hse.gov.uk/pubns/top10noise.pdf UK Health and Safety Executive: Top 10 noise control techniques]</ref>
The perceived loudness of fan noise also depends on the frequency distribution of the noise. This depends on the shape and distribution of moving parts, especially of the blades, and of stationary parts, struts in particular. Like with [[tire tread#Street tires|tire treads]], and similar to the principle of [[Diffusion (acoustics)#Diffusor|acoustic diffusors]], an irregular shape and distribution can flatten the noise spectrum, making the noise sound less disturbing.<ref>{{cite web |title=The Thermodynamics Behind the Mac Pro |url=https://www.popularmechanics.com/technology/gadgets/a30170910/apple-mac-pro/ |website=Popular Mechanics |date=10 December 2019 |access-date=17 December 2019}}</ref><ref> Tae Kim. [https://escholarship.org/uc/item/9q75v9t9 "Reduction of Tonal Propeller Noise by Means of Uneven Blade Spacing"]. p. 4 </ref><ref> M. Boltezar; M. Mesaric; A. Kuhelj. [https://www.sciencedirect.com/science/article/abs/pii/S0022460X98917072 "The influence of uneven blade spacing on the SPL and noise spectra radiated from radial fans"]. </ref>
The inlet shape of the fan can also influence the noise levels generated by the fan.<ref>{{Cite web|url=https://www.nidec.com/en/technology/casestudy/pc/|title = UltraFlo Fluid Dynamic Bearing Fans for Thin Laptop Computers}}</ref>
==Optimal temperature for use== The optimal temperature for using a fan to cool down remains uncertain. While fans are commonly used to lower body temperature through evaporative cooling, there is a point at which the convection effect of moving air can counteract this benefit. This temperature, at which fan use may become detrimental, is currently unknown.<ref name="Cornwall">{{cite news |last=Cornwall |first=Warren |url=https://www.science.org/content/article/when-is-it-too-hot-use-fan |title=When is it too hot to use a fan? |work=[[Science (journal)|Science]] |date=2024-11-06 |access-date=2024-11-09 }}</ref>
Health organizations offer varying guidance on fan usage in high temperatures. The [[Centers for Disease Control and Prevention]] (CDC) advises against fan use when temperatures exceed 32.2 °C (90 °F), while the [[World Health Organization]] (WHO) suggests avoiding fan use above 40 °C (104 °F).<ref name="Cornwall" />
Recent studies have shed further light on this issue, though their findings are somewhat contradictory. One study found limited additional benefit from fan use above 35 °C (95 °F), while another study reported a 31% reduction in cardiac stress among elderly individuals using fans at 38 °C (100 °F).<ref name="Cornwall" />
== Fan motor drive methods == [[File:UMA 2.JPG|thumb|Building heating and cooling systems commonly use squirrel-cage fans driven by separate electric motors connected by belts.]]
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 fan]]s, 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.
The fan is often connected to machines with a rotating part rather than being powered separately. This is commonly seen in motor vehicles with internal combustion engines, 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, other methods may drive fans. High-pressure gases such as steam can drive a small [[turbine]], and high-pressure liquids can 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 required for efficient fan operation.
<gallery> 1989 Toyota 1HD-T Type engine front.jpg|[[Internal combustion engine]]s sometimes drive an engine cooling fan directly or may use a separate electric motor. Silniki by Zureks.jpg|Large electric motors may have a cooling fan either on the back or inside the case. (Shown with the black rear cover removed.) Air conditioning unit-en.svg|Dual shaft fan motor in a window air conditioner </gallery>
== See also == {{columns-list|colwidth=25em| * {{Annotated link|Affinity laws}} * {{Annotated link|Air cooler}} * {{Annotated link|Air purifier}} * {{Annotated link|Attic fan}} * {{Annotated link|Axial fan design}} * {{Annotated link|Compressor}} * {{Annotated link|Corsi–Rosenthal Box}} * {{Annotated link|Evaporative cooler}} * {{Annotated link|Fan heater}} * {{Annotated link|Ion wind}} * {{Annotated link|Specific fan power}} * {{Annotated link|Waddle fan}} * {{Annotated link|Whole-house fan}} * {{Annotated link|Window fan}} }}
== References == {{Reflist}}
== External links == * {{Commons category-inline|Mechanical fans}}
{{HVAC}} {{Home appliances}} {{Automotive engine |collapsed}} {{Authority control}}
[[Category:Ventilation fans| ]] [[Category:Aerodynamics]] [[Category:Articles containing video clips]] [[Category:Cooling technology]] [[Category:Heating, ventilation, and air conditioning]] [[Category:Turbomachinery]] [[Category:Ventilation]]