A fan is a powered machine used to create a flow of

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

. A fan consists of a rotating arrangement of vanes or blades, generally made of

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of ligni ...

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

, or

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typi ...

, which act on the air. The rotating assembly of blades and hub is known as an ''

impeller An impeller or impellor is a rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid. In pumps An impeller is a rotating componen ...

'', ''rotor'', or ''runner''. Usually, it is contained within some form of housing, or case. This may direct the airflow, or increase safety by preventing objects from contacting the fan blades. Most fans are powered by

electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate forc ...

s, but other sources of power may be used, including

hydraulic motor A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement ( rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder as a linear actuator. Most broadl ...

s, handcranks, and

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

s. Mechanically, a fan can be any revolving

vane Vane may refer to: People * Vane (surname) * Vane Featherston (1864–1948), English stage actress * Ivan Vane Ivanović (1913–1999), Yugoslav-British athlete, shipowner, political activist, and philanthropist * Vane Pennell (1876–1938), ...

, or vanes used for producing currents of air. Fans produce air flows with high

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...

and low

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...

(although higher than

ambient pressure Ambient or Ambiance or Ambience may refer to: Music and sound * Ambience (sound recording), also known as atmospheres or backgrounds * Ambient music Ambient music is a genre of music that emphasizes tone and atmosphere over traditional music ...

), as opposed to

compressors A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. Compressors are similar to pumps: both increase the pressure on a fluid and both can trans ...

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 In meteorology, an anemometer () is a device that measures wind speed and direction. It is a common instrument used in weather stations. The earliest known description of an anemometer was by Italian architect and author Leon Battista Alberti ...

s and

wind turbine A wind turbine is a device that converts the kinetic energy of wind into electrical energy. Hundreds of thousands of large turbines, in installations known as wind farms, now generate over 650 gigawatts of power, with 60 GW added each year. W ...

s, often have designs similar to that of a fan. Typical applications include

climate control Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. H ...

and personal

thermal comfort Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation ( ANSI/ASHRAE Standard 55).ANSI/ASHRAE Standard 55-2017, Thermal Environmental Conditions for Human Occupan ...

(e.g., an electric table or floor fan), vehicle engine cooling systems (e.g., in front of a

radiator Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics. A radiator is always a ...

), machinery cooling systems (e.g., inside computers and

audio power amplifier An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals, such as the signal from a radio receiver or an electric guitar pickup, to a level that is high enough for driving loudspea ...

s), ventilation, fume extraction,

winnowing Winnowing is a process by which chaff is separated from grain. It can also be used to remove pests from stored grain. Winnowing usually follows threshing in grain preparation. In its simplest form, it involves throwing the mixture into th ...

(e.g., separating chaff of

cereal A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grain crops are grown in greater quantities and provide more foo ...

grains), removing

dust Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in ...

(e.g.

sucking Suction is the colloquial term to describe the air pressure differential between areas. Removing air from a space results in a pressure differential. Suction pressure is therefore limited by external air pressure. Even a perfect vacuum cannot ...

as in a

vacuum cleaner A vacuum cleaner, also known simply as a vacuum or a hoover, is a device that causes suction in order to remove dirt from floors, upholstery, draperies, and other surfaces. It is generally electrically driven. The dirt is collected by either a ...

), drying (usually in combination with a heat source) and providing draft for a

fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. At a certain point in the combustion reaction, called the ignition ...

. 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, but rather work by

evaporative cooling An evaporative cooler (also known as evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning s ...

sweat Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are dist ...

and increased heat

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

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

The punkah (a.k.a fan) was used in

India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...

about 500 BCE. It was a handheld fan made from bamboo strips or other plant fiber, that could be rotated or fanned to move air. During

British rule The British Raj (; from Hindi ''rāj'': kingdom, realm, state, or empire) was the rule of the British Crown on the Indian subcontinent; * * it is also called Crown rule in India, * * * * or Direct rule in India, * Quote: "Mill, who was himsel ...

, 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 Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...

, the

Han Dynasty The Han dynasty (, ; ) was an Dynasties in Chinese history, imperial dynasty of China (202 BC – 9 AD, 25–220 AD), established by Emperor Gaozu of Han, Liu Bang (Emperor Gao) and ruled by the House of Liu. The dynasty was preceded by th ...

craftsman and engineer

Ding Huan Ding Huan () was a Chinese craftsman, mechanical engineer, and inventor who lived in the first century BC during the Han dynasty. Among the inventions attributed to him is an air conditioning system based on evaporative cooling. Purported inventi ...

(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 The Tang dynasty (, ; zh, t= ), or Tang Empire, was an imperial dynasty of China that ruled from 618 to 907 AD, with an interregnum between 690 and 705. It was preceded by the Sui dynasty and followed by the Five Dynasties and Ten Kingdo ...

(618–907), the Chinese applied hydraulic power to rotate the fan wheels for air conditioning, while the rotary fan became even more common during the

Song Dynasty The Song dynasty (; ; 960–1279) was an imperial dynasty of China that began in 960 and lasted until 1279. The dynasty was founded by Emperor Taizu of Song following his usurpation of the throne of the Later Zhou. The Song conquered the res ...

(960–1279). In the 17th century, the experiments of scientists including

Otto von Guericke Otto von Guericke ( , , ; spelled Gericke until 1666; November 20, 1602 – May 11, 1686 ; November 30, 1602 – May 21, 1686 ) was a German scientist, inventor, and politician. His pioneering scientific work, the development of experimental me ...

Robert Hooke Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that h ...

and

Robert Boyle Robert Boyle (; 25 January 1627 – 31 December 1691) was an Anglo-Irish natural philosopher, chemist, physicist, alchemist and inventor. Boyle is largely regarded today as the first modern chemist, and therefore one of the founders of ...

, established the basic principles of vacuum and airflow. The English architect Sir

Christopher Wren Sir Christopher Wren PRS FRS (; – ) was one of the most highly acclaimed English architects in history, as well as an anatomist, astronomer, geometer, and mathematician-physicist. He was accorded responsibility for rebuilding 52 churc ...

applied an early ventilation system in the

Houses of Parliament The Palace of Westminster serves as the meeting place for both the House of Commons and the House of Lords, the two houses of the Parliament of the United Kingdom. Informally known as the Houses of Parliament, the Palace lies on the north bank ...

that used bellows to circulate air. Wren's design would be 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 Georgius Agricola (; born Georg Pawer or Georg Bauer; 24 March 1494 – 21 November 1555) was a German Humanist scholar, mineralogist and metallurgist. Born in the small town of Glauchau, in the Electorate of Saxony of the Holy Roman Empire ...

(1494–1555).Needham, Volume 4, Part 2, 154.

John Theophilus Desaguliers John Theophilus Desaguliers FRS (12 March 1683 – 29 February 1744) was a British natural philosopher, clergyman, engineer and freemason who was elected to the Royal Society in 1714 as experimental assistant to Isaac Newton. He had studied at ...

, a British engineer, demonstrated the successful use of a fan system to draw out stagnant air from coal mines in 1727 and soon afterward he installed a similar apparatus in Parliament. Good ventilation was particularly important in coal mines to reduce casualties from asphyxiation. The civil engineer

John Smeaton John Smeaton (8 June 1724 – 28 October 1792) was a British civil engineer responsible for the design of bridges, canals, harbours and lighthouses. He was also a capable mechanical engineer and an eminent physicist. Smeaton was the firs ...

, and later

John Buddle John Buddle (15 September 1773 – 10 October 1843) was a prominent self-made mining engineer and entrepreneur in North East England. He had a major influence on the development of the Northern Coalfield in the first half of the 19th century, c ...

installed reciprocating air pumps in the mines in the North of

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

. However, this arrangement was not as ideal as the machinery was liable to breaking down.

Steam

In 1849 a 6m radius steam-driven fan, designed by

William Brunton William Brunton Senior (26 May 1777 – 5 October 1851) was a Scottish engineer and inventor. Early life He was the eldest son of Robert Brunton, a watchmaker (14 Aug 1748–1834) of Dalkeith, where he was born. He studied mechanics in his fath ...

, was made operational in the Gelly Gaer

Colliery Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron fro ...

South Wales South Wales ( cy, De Cymru) is a loosely defined region of Wales bordered by England to the east and mid Wales to the north. Generally considered to include the historic counties of Glamorgan and Monmouthshire, south Wales extends westwards ...

. The model was exhibited at the

Great Exhibition The Great Exhibition of the Works of Industry of All Nations, also known as the Great Exhibition or the Crystal Palace Exhibition (in reference to the temporary structure in which it was held), was an international exhibition which took pl ...

of 1851. Also in 1851

David Boswell Reid Prof David Boswell Reid MD FRSE FRCPE (1805 – 5 April 1863) was a British physician, chemist and inventor. Through reports on public hygiene and ventilation projects in public buildings, he made a reputation in the field of sanitation. He has ...

, a Scottish doctor, installed four steam-powered fans in the ceiling of

St George's Hospital St George's Hospital is a large teaching hospital in Tooting, London. Founded in 1733, it is one of the UK's largest teaching hospitals and one of the largest hospitals in Europe. It is run by the St George's University Hospitals NHS Foundatio ...

Liverpool Liverpool is a City status in the United Kingdom, city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the List of English districts by population, 10th largest English district by population and its E ...

, so that the pressure produced by the fans would force the incoming air upward and through vents in the ceiling. Improvements in the technology were made by

James Nasmyth James Hall Nasmyth (sometimes spelled Naesmyth, Nasmith, or Nesmyth) (19 August 1808 – 7 May 1890) was a Scottish engineer, philosopher, artist and inventor famous for his development of the steam hammer. He was the co-founder of Nasmyth, ...

, Frenchman Theophile Guibal and J. R. Waddle.

Electrical

Between 1882 and 1886

Schuyler Wheeler Schuyler Skaats Wheeler (May 17, 1860 – April 20, 1923) was an American electrical engineer Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use ...

invented a fan powered by electricity. 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. In 1882, Philip Diehl developed the world's first electric 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. By the 1940s,

Crompton Greaves Crompton Greaves Consumer Electricals Limited (also known as Crompton) is an Indian electrical equipment company based in Mumbai, India. The company has lighting and electrical consumer durables including LED lighting, fans, pumps, and house ...

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 eye-catching. Window and central

in the 1960s caused many companies to discontinue production of fans,Fancollectors.org – A Brief History of Fans
Information Provided by Steve Cunningham – retrieved July 5, 2010. 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 immensely popular again as both decorative and energy-efficient units. In 1998 William Fairbank and Walter K. Boyd invented the 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.Industrial Fan Designer Finds Niche in Energy Efficiency – Automation and Control
By David Greenfield, December 20, 2010, Blog on Design News, Information provided by Dianna Huff – retrieved May 18, 2011.

Types

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). They can also be built into a

window A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent mate ...

, wall, roof, chimney, etc. Most electronic systems such as computers include fans to cool the circuits inside, and in appliances such as hair dryers and portable space heaters and mounted/installed wall heaters. They are also used for moving air in air-conditioning systems, and in automotive engines, where they are driven by belts or by a direct motor. Fans used for comfort create a

wind chill Wind chill or windchill (popularly wind chill factor) is the lowering of body temperature due to the passing-flow of lower-temperature air. Wind chill numbers are always lower than the air temperature for values where the formula is valid. When ...

by increasing the

heat transfer coefficient In thermodynamics, the heat transfer coefficient or film coefficient, or film effectiveness, is the proportionality constant between the heat flux and the thermodynamic driving force for the flow of heat (i.e., the temperature difference, ). ...

but do not lower temperatures directly. Fans used to cool electrical equipment or in engines or other machines do cool the equipment directly by forcing hot air into the cooler environment outside of the machine. There are three main types of fans used for moving air, ''axial'', ''centrifugal'' (also called ''radial'') and ''cross flow'' (also called ''tangential''). The American Society of Mechanical Engineers Performance Testing Code 11 (PTC)ASME PTC 11 – Fans
provides standard procedures for conducting and reporting tests on fans, including those of the centrifugal, axial, and mixed flows.

Axial-flow

Axial-flow fans have blades that force air to move

parallel Parallel is a geometric term of location which may refer to: Computing * Parallel algorithm * Parallel computing * Parallel metaheuristic * Parallel (software), a UNIX utility for running programs in parallel * Parallel Sysplex, a cluster of I ...

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 towers A cooling tower is a device that rejects waste heat to the atmosphere through the cooling of a coolant stream, usually a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and ...

. 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 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 Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is co ...

s, motor, blade 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 to 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 to 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, whilst kitchen extractor fans typically use a six-inch (150 mm) impeller as the room itself is often bigger. Axial fans with five-inch (125 mm) impellers are also used in larger bathrooms though are much less common. Domestic axial extractor fans are not suitable 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 performance of the fan

* Electro-mechanical fans: Among collectors, are rated according to their condition, size, age, and several 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. *

Ceiling fan A ceiling fan is a fan mounted on the ceiling of a room or space, usually electrically powered, that uses hub-mounted rotating blades to circulate air. They cool people effectively by increasing air speed. Fans do not reduce air temperatur ...

: A fan suspended from the ceiling of a room is a ceiling fan. Most ceiling fans rotate at relatively low speeds and do not have blade guards. Ceiling fans can be found in both residential and industrial/commercial settings. * In

automobile A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded ...

s, a mechanical or electrically driven fan provides

engine cooling Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple sys ...

and prevents the engine from overheating by blowing or drawing air through a

coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corros ...

-filled

. The fan may be driven with a belt and pulley off the

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...

's crankshaft or an electric motor switched on or off by a

thermostat A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint. Thermostats are used in any device or system tha ...

switch In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type ...

. *

Computer fan A computer fan is any fan inside, or attached to, a computer case used for active cooling. Fans are used to draw cooler air into the case from the outside, expel warm air from inside and move air across a heat sink to cool a particular compon ...

for cooling electrical components and in laptop coolers * Fans inside

s help to draw heat away from the electrical components. * Variable pitch fan: A variable-pitch fan is used where precise control of static pressure within supply ducts is required. 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

Often called a "squirrel cage" (because of its general similarity in appearance to exercise wheels for pet rodents) or "scroll fan", the centrifugal fan has a moving component (called an

) that consists of a central shaft about which a set of blades that form a

spiral In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point. Helices Two major definitions of "spiral" in the American Heritage Dictionary are:centrifugal force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is parallel ...

). The impeller rotates, causing air to enter the fan near the shaft and move

perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...

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 A leaf blower, commonly known as a blower, is a device that propels air out of a nozzle to move debris such as leaves and grass cuttings. Leaf blowers are powered by electric or gasoline motors. Gasoline models have traditionally been two-str ...

blowdryer A hair dryer, hairdryer or blow dryer is an electromechanical device that blows ambient or hot air over damp hair to speed the evaporation of water to dry the hair. Blow dryers enable better control over the shape and style of hair, by accelera ...

s, air mattress inflators, inflatable structures,

in 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). 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 an HP ZBook mobile workstation laptop. The fan displaces air over the fin-stack which contain a pair of heatpipes

Cross-flow

The ''cross-flow'' or ''tangential'' fan, sometimes known as a ''tubular'' fan, was patented in 1893 by Paul Mortier, and is used extensively in

heating, ventilation, and air conditioning Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. ...

(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

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. 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. 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. 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 A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...

s (pressure decrease). Since the flow both enters and exits the impeller radially, the crossflow fan has been studied and prototyped for potential aircraft applications. 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 The leading edge of an airfoil surface such as a wing is its foremost edge and is therefore the part which first meets the oncoming air.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, ...

is the

FanWing The FanWing is an aircraft configuration in which a horizontal-axis cross-flow fan is used in close conjunction with a fixed wing. The fan forces airflow over the fixed surface to provide both lift and forward thrust. The concept was initially de ...

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 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 The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 199 ...

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. Cross-flow fans are made to have a double circular arc rear wall with a thick vortex wall that decreases in radial gap. The gap decreases in the direction of the fans impeller rotation. The rear wall has a log-spiral profile while the vortex stabilizer is a horizontal thin wall with rounded edge. 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 Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...

air door An air door or air curtain is a device used to prevent air, contaminants, or flying insects from moving from one open space to another. The most common implementation is a downward-facing blower fan mounted over an entrance to a building, or ove ...

s, in some types of laptop coolers, in automobile ventilation systems, and for cooling in medium-sized equipment such as

photocopier A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopiers u ...

Bladeless fans

Dyson Air Multiplier fans introduced to the consumer market in 2009 have popularized a 1981 design by

Toshiba , commonly known as Toshiba and stylized as TOSHIBA, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. Its diversified products and services include power, industrial and social infrastructure systems ...

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). 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 An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or tur ...

surface shape (the

Coandă effect The Coandă effect ( or ) is the tendency of a fluid jet to stay attached to a convex surface. ''Merriam-Webster'' describes it as "the tendency of a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to en ...

). 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 described in this article hidden in the base of the display cabinet.

HVAC Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. ...

linear slot diffusers also utilize this effect to increase airflow evenly in rooms compared to registers while reducing the energy used by the

air handling unit An air handler, or air handling unit (often abbreviated to AHU), is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blowe ...

blower.

Installation

Fans may be installed in various ways, according to the application. They are often used in a free installation, without any housing of any kind. There are also some specialised installations.

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 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.

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 dB. The perceived loudness of fan noise also depends on the frequency distribution of the noise. This in turn depends on the shape and distribution of moving parts, especially of the blades, and of stationary parts, struts in particular. Like with tire treads, and similar to the principle of acoustic diffusors, an irregular shape and distribution can flatten the noise spectrum, making the noise sound less disturbing. The inlet shape of the fan can also influence on the noise levels generated by the fan.

Fan motor drive methods

Standalone fans are usually powered by an

, 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 belt and pulleys. Smaller fans are often powered by shaded pole AC motors, or brushed or

brushless DC motors A brushless DC electric motor (BLDC motor or BL motor), also known as an electronically commutated motor (ECM or EC motor) or synchronous DC motor, is a synchronous motor using a direct current (DC) electric power supply. It uses an electron ...

. AC-powered fans usually use mains voltage, while DC-powered fans typically use low voltage, typically 24V, 12V, or 5 V. 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

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

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

, and high-pressure liquids can be used to drive a

pelton wheel The Pelton wheel or Pelton Turbine is an Impulse (physics), impulse-type water turbine invented by American inventor Lester Allan Pelton in the 1870s. The Pelton wheel extracts energy from the impulse of moving water, as opposed to water's dead w ...

, either 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 A water wheel is a machine for converting the energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a wheel (usually constructed from wood or metal), with a number of blades or buck ...

and a series of step-down gears or pulleys to increase the rotational speed to that which is required for efficient fan operation. 1989 Toyota 1HD-T Type engine front.jpg,

Internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal co ...

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

Solar power

Electric fans used for ventilation may be powered by

solar panels A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a phot ...

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. Also, electricity is always available when the sun is shining and the fan needs to run. During the absence of electric power solar powered fan is operate the air flowing and maintain environmental condition. A typical example uses a detached 10-

watt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...

, solar panel and is supplied with appropriate brackets,

cables Cable may refer to: Mechanical * Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof * Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...

, and connectors. It can be used to ventilate up to of

area Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape or planar lamina, while ''surface area'' refers to the area of an open su ...

and can move air at up to . Because of the wide availability of 12 V

brushless DC electric motor A brushless DC electric motor (BLDC motor or BL motor), also known as an electronically commutated motor (ECM or EC motor) or synchronous DC motor, is a synchronous motor using a direct current (DC) electric power supply. It uses an electron ...

s and the convenience of wiring such a low voltage, such fans usually operate on 12

volt The volt (symbol: V) is the unit of electric potential, electric potential difference ( voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). D ...

s. The detached solar panel is typically installed in the spot which gets most of the sunlight and then connected to the fan mounted as far as away. Other permanently-mounted and small portable fans include an integrated (non-detachable) solar panel.

References

External links

* {{Authority control Turbomachinery Cooling technology Ventilation Heating, ventilation, and air conditioning Mechanical engineering Chemical engineering Gas compressors Turbines Thermodynamics Fluid dynamics Aerodynamics Articles containing video clips