Mechanical fan

Household electric “box” fan with a propeller style blade

Amechanical fan is a machine used to create flowwithina fluid, typically a gas such as air.[1] The fan consists of arotating arrangement of vanes or blades which act on thefluid. The rotating assembly of blades and hub is knownas an impeller, a rotor, or a runner. Usually, it is con-tained within some form of housing or case.[2] This maydirect the airflow or increase safety by preventing objectsfrom contacting the fan blades. Most fans are poweredby electric motors, but other sources of power may beused, including hydraulic motors and internal combus-tion engines. Fans produce flows with high volume andlow pressure (although higher than ambient pressure), asopposed to compressors which produce high pressures ata comparatively low volume. A fan blade will often rotatewhen exposed to a fluid stream, and devices that take ad-vantage of this, such as anemometers and wind turbines,often have designs similar to that of a fan.For more details on this topic, see Centrifugal compres-sor.

Typical applications include climate control and personalthermal comfort (e.g., an electric table or floor fan), ve-hicle and machinery cooling systems, ventilation, fume

A household electric floor fan

extraction, winnowing (e.g., separating chaff of cerealgrains), removing dust (e.g. in a vacuum cleaner), dry-ing (usually in combination with heat) and to providedraft for a fire. While fans are often used to cool peo-ple, they do not actually cool air (if anything, electricfans warm it slightly due to the warming of their motors),but work by evaporative cooling of sweat and increasedheat convection into the surrounding air due to the air-flow from the fans. Thus, fans may become ineffective atcooling the body if the surrounding air is near body tem-perature and contains high humidity. In addition to theirutilitarian function, vintage or antique fans, and in partic-ular electric fans manufactured from the late 19th centurythrough the 1950s, have become a recognized collectiblecategory; for example, in the U.S.A. there is the AntiqueFan Collectors Association.[3]

1

2 3 TYPES OF FANS

1 Etymology

The word fan comes from Middle English, winnowingfan, from Old English fann and from Latin vannus.[1]

2 History

The punkah fan was used in India in the early 500 BC.It was a handheld fan made from bamboo strips or otherplant fibre, that could be rotated or fanned. During Britishrule, the word came to be used in a special sense byAnglo-Indians to mean a large swinging fan, fixed to theceiling, and pulled by a servant, called the punkawallah.

Patent drawing for a Fan Moved by Mechanism, 27 November1830

In the 17th century, the experiments of scientists likeOtto von Guericke, Robert Hooke and Robert Boyle, elu-cidated the principles of vacuum and airflow. The Englisharchitect Sir Christopher Wren applied an early ventila-tion system in the Houses of Parliament that used bellowsto circulate the air. The Houses of Parliament would bethe catalyst for much later improvement and innovation.John Theophilus Desaguliers, a British engineer, demon-strated a successful use of a fan system to draw out stag-nant air from the coal mines in 1727 and soon afterwardshe installed a similar apparatus in Parliament.[4] Goodventilation was particularly important in the coal minesto reduce miner casualties from gas asphyxiation. Thecivil engineer John Smeaton, and later John Buddle in-stalled reciprocating air pumps in the mines in the Northof England. However, this arrangement was not ideal asthe machinery was liable to breaking down. With the ad-vent of practical steam power, fans could finally be usedfor ventilation. David Boswell Reid, a Scottish physi-cian, installed four steam powered fans in the ceiling ofSt George’s Hospital in Liverpool, so that the pressureproduced by the fans would force the incoming air up-ward and through vents in the ceiling.[5] In 1849 a 6mradius 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 Exhibi-tion of 1851. Improvements in the technology were madeby James Nasmyth, Frenchman Theophile Guibal and J.R. Waddle.[6] Between the years 1882 and 1886, NewOrleans resident Schuyler Skaats Wheeler invented a fanpowered by electricity.[7] It was commercially marketedby the American firm Crocker & Curtis electric motorcompany. In 1882, Philip Diehl introduced the electricceiling fan. Heat-convection fans fueled by alcohol, oil,or kerosene were common around the turn of the 20thcentury.

A 6 blade HVLS fan.

In the 1920s, industrial advances allowed steel fans to bemass-produced in different shapes, bringing fan pricesdown and allowing more homeowners to afford them. Inthe 1930s, the first art deco fan (the “swan fan”) was de-signed. In the 1950s, fans were manufactured in colorsthat were bright and eye catching. Central air condition-ing in the 1960s caused many companies to discontinueproduction of fans.[8] In the 1970s, Victorian-style ceilingfans became popular. In 1998, Walter K. Boyd inventedthe HVLS ceiling fan. Boyd developed a slow moving fanwith a very large 8-feet diameter. Due to its size, the fanmoved a large column of air down and out 360 degreesand continuously mixed fresh air with the stale air insidethe barn. They are used in many industrial settings, be-cause of their energy efficiency.[9]

3 Types of fans

Mechanical revolving blade fans are made in a wide rangeof designs. In a home you can find fans that can be puton the floor or a table, or hung from the ceiling, or arebuilt into a window, wall, roof, chimney, etc. They canbe found in electronic systems such as computers wherethey cool the circuits inside, and in appliances such as hairdryers and portable space heaters and mounted/installedwall heaters. They are also used for moving air in air-conditioning systems, and in automotive engines, wherethey are driven by belts or by direct motor. Fans used forcomfort create a wind chill, but do not lower tempera-tures directly. Fans used to cool electrical equipment or

3.2 Centrifugal fan 3

Two c. 1980 box fans

Ceiling fan with lamp

in engines or other machines do cool the equipment di-rectly by forcing hot air into the cooler environment out-side the machine. There are three main types of fans usedfor moving air, axial, centrifugal (also called radial) andcross flow (also called tangential).

3.1 Axial-flow fans

An axial box fan for cooling electrical equipment

Axial-flow fans have blades that force air to move parallel

to the shaft about which the blades rotate. Axial fans blowair along the axis of the fan, linearly, hence their name.This type of fan is used in a wide variety of applications,ranging from small cooling fans for electronics to the giantfans used in wind tunnels. Axial flow fans are appliedfor air conditioning and industrial process applications.Standard axial flow fans have diameters from 300–400mm or 1800 to 2000 mm and work under pressures up to800 Pa. Examples of axial fans are:

• Table fan: Basic elements of a typical table fan in-clude the fan blade, base, armature and lead wires,motor, blade guard, motor housing, oscillator gear-box, and oscillator shaft. The oscillator is a mecha-nism that moves the fan from side to side. The axlecomes out on both ends of the motor, one end of theaxle is attached to the blade and the other is attachedto the oscillator gearbox. Themotor case joins to thegearbox to contain the rotor and stator. The oscilla-tor shaft combines to the weighted base and the gear-box. A motor housing covers the oscillator mecha-nism. The blade guard joins to the motor case forsafety.

• Ceiling fan: A fan suspended from the ceiling of aroom is a ceiling fan. Ceiling fans can be found inboth residential and industrial/commercial settings.

• In automobiles, a mechanical fan provides enginecooling and prevents the engine from overheatingby blowing or sucking air through a coolant-filledradiator. It can be driven with a belt and pulley offthe engine's crankshaft or an electric fan switchedon or off by a thermostatic switch.

• Computer cooling fan for cooling electrical compo-nents

• Variable Pitch Fan: A variable-pitch fan is usedwhere precise control of static pressure within sup-ply ducts is required. The blades are arranged torotate upon a control-pitch hub. The fan wheel willspin at a constant speed. As the hub moves towardthe rotor, the blades increase their angle of attackand an increase in flow results.

3.2 Centrifugal fan

Main article: centrifugal fanOften called a “squirrel cage” (because of its similar-ity in appearance to exercise wheels for pet rodents) or“scroll fan”, the centrifugal fan has a moving component(called an impeller) that consists of a central shaft aboutwhich a set of blades, or ribs, are positioned. Centrifu-gal fans blow air at right angles to the intake of the fan,and spin the air outwards to the outlet (by deflection andcentrifugal force). The impeller rotates, causing air to en-ter the fan near the shaft and move perpendicularly fromthe shaft to the opening in the scroll-shaped fan casing.

4 4 UNCOMMON TYPES OF FAN

Typical centrifugal fan

A centrifugal fan produces more pressure for a given airvolume, and is used where this is desirable such as inleaf blowers, blowdryers, air mattress inflators, inflatablestructures, climate control, and various industrial pur-poses. They are typically quieter than comparable axialfans.

3.3 Cross-flow fan

Cross-section of cross-flow fan, from the 1893 patent. The ro-tation is clock-wise. The stream guide F is usually not present inmodern implementations.

Cross-flow fan

The cross-flow or tangential fan, sometimes known as a

tubular fan was patented in 1893 by Paul Mortier,[10] andis used extensively in the HVAC industry. The fan is usu-ally long in relation to the diameter, so the flow approx-imately remains two-dimensional away from the ends.The CFF uses an impeller with forward curved blades,placed in a housing consisting of a rear wall and vortexwall. Unlike radial machines, the main flow moves trans-versely across the impeller, passing the blading twice.The flow within a cross-flow fan may be broken up intothree distinct regions: a vortex region near the fan dis-charge, called an eccentric vortex, the through-flow re-gion, and a paddling region directly opposite. Both thevortex and paddling regions are dissipative, and as a re-sult, only a portion of the impeller imparts usable work onthe flow. The cross-flow fan, or transverse fan, is thus atwo-stage partial admission machine. The popularity ofthe crossflow fan in the HVAC industry comes from itscompactness, shape, quiet operation, and ability to pro-vide high pressure coefficient. Effectively a rectangularfan in terms of inlet and outlet geometry, the diameterreadily scales to fit the available space, and the length isadjustable to meet flow rate requirements for the partic-ular application. Common household tower fans are alsocross-flow fans.Much of the early work focused on developing the cross-flow fan for both high and low-flow-rate conditions, andresulted in numerous patents. Key contributions weremade by Coester, Ilberg and Sadeh, Porter andMarkland,and Eck.One 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 ascompressors (pressure increase), while at other azimuthallocations the blades act as turbines (pressure decrease).

4 Uncommon types of fan

4.1 Bellows

Main article: BellowsBellows are also used to move air, although not generallyconsidered fans. A hand-operated bellows is essentially abag with a nozzle and handles, which can be filled with airby one movement, and the air expelled by another. Typ-ically it would comprise two rigid flat surfaces hinged atone end, where a nozzle is fitted, and with handles at theother. The sides of the surfaces are joined by a flexibleand air-proof material such as leather; the surfaces andjoining material comprise a bag sealed everywhere but atthe nozzle. (The joining material typically has a charac-teristic pleated construction that is so common that sim-ilar expanding fabric arrangements not used for movingair, such as on a folding camera, are called bellows.) Sep-arating the handles expands the bag, which fills with air;squeezing them together expels the air. A simple valve(e.g., a flap) may be fitted so that air enters without hav-

4.3 Convective 5

Diagram of a single-acting hand bellows

ing to come from the nozzle, which may be close to a fire.Bellows produce a directed pressurized stream of air; theairflow volume is typically low with moderate pressure.They are an older technology, used mainly to produce astrong and directed airflow unlike non-electric bladedme-chanical fans, before the introduction of electricity.

• A single-acting bellows will only produce airflowduring the exhaust stroke.

• A double-acting bellows is a pair of bellows capableof blowing out air from one while inhaling air intothe other, but airflow still temporarily ceases whenthe stroke direction is reversed.

• Combining multiple bellows at third-cycle orquarter-cycle arrangements on a crank arm allowsfor nearly continuous airflow from several bellowsat once; each is in a different phase of inhaling andexhausting during the cycle.

4.2 Coandă effect

The Dyson Air Multiplier fans, and the Imperial C2000series range hood fans,[11] have no exposed fan blades orother visibly moving parts. The airflow is generated us-ing the Coandă effect; a small quantity of air from a high-pressure bladed impeller fan, contained in the base ratherthan exposed, drives a large airmass via a low-pressurearea created by the airfoil.[12][13][14] The US Patent &Trademark Office initially ruled that Dyson’s patent wasnot an improvement on the Toshiba patent on a nearlyidentical bladeless desktop fan granted in 1981.[12] Aircurtains and air doors also utilize this effect to help re-tain warm or cool air within an otherwise exposed area

An open-face supermarket freezer with an air curtain. Coolingair circulates across the food through the dark slot seen at therear of the freezer, and through another grille not visible alongthe front.

that lacks a cover or door. Air curtains are commonlyused on open-face dairy, freezer, and vegetable displaysto help retain chilled air within the cabinet using a lami-nar airflow circulated across the display opening, usuallygenerated by a fan in the base of the cabinet.

4.3 Convective

Differences in air temperature will affect the density ofair and can be used to induce air circulation through themere act of heating or cooling an air mass. This effect isso subtle and works at such low air pressures that it doesnot appear to fit the definition of a fan technology. How-ever, prior to the development of electricity, convectiveairflow was the primary method of inducing airflow in liv-ing spaces. Old fashioned oil and coal furnaces were notelectric and operated simply on the principle of convec-tion to move the warm air. Very large volume air ductswere sloped upwards away from the top of the furnacetowards floor and wall registers above the furnace. Coolair was returned through similar large ducts leading to thebottom of the furnace. Older houses from before electri-fication often had open duct grilles leading from the ceil-ing of a lower level to the floor of an upper level, to allowconvective airflow to slowly rise up the building from onefloor to the next. Outhouses commonly rely on a sim-ple enclosed air channel in a corner of the structure toexhaust offensive odors. Exposed to sunlight, the chan-nel is warmed and a slow convective air current is ventedout the top of the building, while fresh air enters the pitthrough the seat hole.

4.4 Electrostatic

An electrostatic fluid accelerator propels airflow by induc-ing motion in airborne charged particles. A high voltageelectric field (commonly 25,000 to 50,000 volts) formed

6 6 FAN DRIVE METHODS

between exposed charged anode and cathode surfaces iscapable of inducing airflow through a principle referredto as ionic wind. The airflow pressure is typically verylow but the air volume can be large. However, a suffi-ciently high voltage potential can also cause the forma-tion of ozone and nitrogen oxides, which are reactive andirritating to mucous membranes.

5 Noise

Fans generate noise from the rapid flow of air aroundblades and obstacles, and sometimes from the motor. Fannoise has been found to be roughly proportional to thefifth power of fan speed; halving speed reduces noise byabout 15dB.[15]

6 Fan drive methods

Building heating and cooling systems commonly use a squirrelcage fan driven by belt from a separate electric motor.

Internal combustion engines sometimes drive an engine coolingfan directly, or may use a separate electric motor.

Standalone fans are usually powered by electric motors,often attached directly to the motor’s output with no gears

Large electric motors may have a cooling fan either on the backor inside the case. (Shown with black rear cover removed.)

INDOORS

OUTDOORS

Blower

Cooled air

Cooling coilsIndoor air

Outdoor air

Hot air

Condenser coils

Fan

Fan axle

Compressor

Expansion valve

Temperature sensing bulb

Dual shaft fan motor in a window air conditioner.

or belts. The motor is either hidden in the fan’s centerhub or extends behind it. For big industrial fans, three-phase asynchronous motors are commonly used, placednear the fan and driving it through a belt and pulleys.Smaller fans are often powered by shaded pole AC mo-tors, or brushed or brushless DC motors. AC-poweredfans usually use mains voltage, while DC-powered fansuse low voltage, typically 24, 12, or 5 V. Cooling fansfor computer equipment always use brushless DC mo-tors, which generate much less electromagnetic interfer-ence than other types. In machines with a rotating part,the fan is often connected to it rather than being poweredseparately. This is commonly seen in motor vehicles withinternal combustion engines, where the fan is connectedto the drive shaft directly or through a belt and pulleys. Acommon configuration is a dual-shaft motor, where oneend of the shaft drives a mechanism, while the other hasa fan mounted on it to cool the motor itself. Windowair conditioners commonly use a dual-shaft fan to oper-ate separate blowers for the interior and exterior parts ofthe device. Where electrical power or rotating parts arenot available, fans may be drive by other methods. High-pressure gases such as steam can be used to drive a smallturbine, and high-pressure liquids can be used to drive apelton wheel, which can provide the rotational drive for a

7

fan. Large, slow-moving energy sources such as a flowingriver can also power a fan using a water wheel and a trainof gears or pulleys.

7 See also• Affinity laws

• Axial fan design

• Air cooler

• Balancing machine

• Fan death

• Industrial fans

• Pump

• Specific fan power

• Waddle fan

• Whole-house fan

8 References[1] “Fan”. The Free Dictionary By Farlex. Retrieved 2012-

05-19.

[2] “Fan”. Britannica. Retrieved 2012-05-19.

[3] Antique Fan Collectors Association website

[4] “A Short History of Mechanical Fans”. The WorshipfulCompany of Fan Makers.

[5] Robert Bruegmann. “Central Heating and Ventilation:Origins and Effects on Architectural Design”.

[6] Cory, William (2010). Fans and Ventilation: A practicalguide. Elsevier.

[7] “B. A. C. (Before Air Conditioning)". New Orleans BarAssociation.

[8] Fancollectors.org - A Brief History of Fans InformationProvided by Steve Cunningham - retrieved July 5, 2010.

[9] Information provided by Dianna Huff - retrieved May 18,2011.

[10] Paul Mortier. Fan or Blowing apparatus. US Pat. No.507,445

[11]

[12] Wallop, Harry (20 October 2009). “Dyson fan: was itinvented 30 years ago?". The Daily Telegraph (London).

[13]

[14] Video

[15] UK Health and Safetey Executive: Top 10 noise controltechniques

9 External links• Media related to Fans (mechanical) at WikimediaCommons

8 10 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

10 Text and image sources, contributors, and licenses

10.1 Text• Mechanical fan Source: http://en.wikipedia.org/wiki/Mechanical%20fan?oldid=634049435 Contributors: Europrobe, Jpatokal, Han-kwang, Auric, DocWatson42, Antandrus, Kaldari, Klaas van Aarsen, Discospinster, Adam850, Meggar, Mdd, OGoncho, Alansohn, Atlant,Velella, Pol098, Firien, Mandarax, SqueakBox, Graham87, Bruce1ee, Vegaswikian, DMahalko, Me and, CambridgeBayWeather, Dhollm,NeilN, SmackBot, Melchoir, Sea diver, Hengsheng120, Keith Lehwald, Snowmanradio, Bobbie4, Crd721, KLLvr283, John, Retromaniac,P199, Peter Horn, Shoeofdeath, Ewulp, Owen214, Vaughnstull, Chrike, Besieged, Gogo Dodo, Studerby, Arb, Thijs!bot, Dtgriscom, Bob-blehead, Escarbot, JAnDbot, Barek, MER-C, Bkpsusmitaa, Connormah, Father Goose, Tedickey, Avicennasis, Vssun, Gun Powder Ma,Scottmacpherson, Flowanda, Smial, J.delanoy, Darthvader1, Tntdj, McSly, Fountains of Bryn Mawr, Bigdumbdinosaur, Squids and Chips,Funandtrvl, Vranak, Philip Trueman, Mkoronowski, Andy Dingley, Synthebot, Lova Falk, Sesshomaru, Michael Frind, S8333631, SieBot,Krfx, Mik93, Martarius, The Thing That Should Not Be, CharlesYin96, Remag Kee, Auntof6, Pointillist, Quercus basaseachicensis, Eeek-ster, Dfsghjkgfhdg, Iohannes Animosus, Thingg, Holav, DumZiBoT, Bridies, Delicious carbuncle, Dthomsen8, LakeAtNight, Alexius08,Sweetpoet, Sameer0s, Kbdankbot, Addbot, Betterusername, Thomas Guibal, JeanLatore, Dizzyspydr, SpillingBot, Cst17, Tide rolls, Light-bot, OKD, Nguyễn Thanh Quang, Gail, Arbitrarily0, Luckas-bot, Rios, Darx9url, Dmarquard, AnomieBOT, Ciphers, Rubinbot, DanielePugliesi, Materialscientist, Teresa Roanoke, RibotBOT, CHJL, Yoganate79, FrescoBot, RexWang, RedBot, Peter.schild, Gamewizard71,FoxBot, Strojar 88, Reaper Eternal, Some Wiki Editor, Minimac, DARTH SIDIOUS 2, RjwilmsiBot, AeroEng24, Moggyland, JackSchlederer, DASHBot, EmausBot, Apricot50, Tommy2010, Knight1993, Muslim Editor, Noodleki, Moseyman, Autoerrant, Jcaraballo,Peter Karlsen, Juniorjimmy88, ResearchRave, ClueBot NG, Djhuff, Movses-bot, ReyRichard, Widr, GlassLadyBug, ManChild997, Neil-isyours, Jorgenev, Ventilationfans, WNYY98, A. McCartney, BG19bot, Samvith2011, Sarahliaoye, Dan653, Mark Arsten, Stupidfatman,TheeLuk3Miller, Tomo211, Prj1991, BuzyBody, Saehry, Frosty, Epicgenius, CsDix, Tentinator, Basji, V-Guard Industries, Thisiswhy-wecanthavenicethings, Param Mudgal, Ellice sfvorez45, Lemonsmeller, Moep621, Eggs247, Vieque, Ananian, Nittesh99, Bobisthebest9,Subashkhatiwada56 and Anonymous: 167

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