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A fan is a powered
machine A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular machine that uses Power (physics), power to apply Force, forces and control Motion, moveme ...

machine
used to create a flow of
air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of the atmosphere (0.04402961% at April 2019 concentration ). Number ...

air
. A fan consists of a rotating arrangement of vanes or
blades
blades
, generally made of
wood Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. ...

wood
,
plastic Plastics are a wide range of syntheticA synthetic is an artificial material produced by organic chemistry, organic chemical synthesis. Synthetic may also refer to: In the sense of both "combination" and "artificial" * Synthetic chemical or s ...

plastic
, or
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
, which act on the air. The rotating assembly of blades and hub is known as an ''
impeller An impeller or impellor is a wikt:rotor#English, 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 ...

impeller
'', ''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
electric motor
s, but other sources of power may be used, including
hydraulic motor A hydraulic motor is a mechanical actuatorAn actuator is a component of a machine A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular mach ...
s,
handcrank A crank is an arm attached at a right angle to a rotating shaft by which circular motion is imparted to or received from the shaft. When combined with a connecting rod, it can be used to convert circular motion into reciprocating motion, or vice ...
s, and
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and ...

internal combustion engine
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), Engl ...

vane
, or vanes used for producing currents of air. Fans produce air flows with high
volume Volume is a scalar quantity expressing the amount Quantity or amount is a property that can exist as a multitude Multitude is a term for a group of people who cannot be classed under any other distinct category, except for their shared fact ...

volume
and low
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mass to change its velocity (e.g. moving fr ...

pressure
(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, a genre of music that puts an emphasis on tone and atmosphere * ''Ambient'' (album), by Moby * ...
), as opposed to
compressors A compressor is a mechanical device that increases the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, fr ...
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 An anemometer is a device used for measuring wind speed and wind direction, direction. It is also a common weather station instrument. The term is derived from the Greek word ''anemos'', which means wind, and is used to describe any wind speed in ...

anemometer
s and
wind turbine A wind turbine is a device that converts Religious conversion is the adoption of a set of beliefs identified with one particular religious denomination A religious denomination is a subgroup within a religion Religion is a social s ...

wind turbine
s, often have designs similar to that of a fan. Typical applications include
climate control Heating, ventilation, and air conditioning (HVAC) is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical eng ...

climate control
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 Occupanc ...
(e.g., an electric table or floor fan), vehicle engine cooling systems (e.g., in front of a
radiator Radiators are heat exchanger A heat exchanger is a system used to transfer heat between two or more fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or externa ...

radiator
), 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 radio receiver or electric guitar pickup (music technology), pickup to a level that is high enough for ...
s), ventilation, fume extraction,
winnowing Winnowing is a process by which chaff Chaff (; ) is the dry, scaly protective hull (botany), casing of the seeds of cereal grains, or similar fine, dry, scaly plant material such as scaly parts of flowers, or finely chopped straw. Chaff i ...

winnowing
(e.g., separating chaff of
cereal A cereal is any grass cultivated (grown) for the edible components of its grain A grain is a small, hard, dry seed, with or without an attached husk, hull or fruit layer, harvested for human or animal consumption. A grain crop is a grain-pro ...

cereal
grains), removing
dust Dust is made of s of solid . On Earth, it generally consists of particles in the that come from various sources such as lifted by wind (an ), , and . Dust in homes is composed of about 20–50% dead . The rest, and in offices, and other ...
(e.g.
sucking Suction is the force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), moti ...
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 d ...

vacuum cleaner
), drying (usually in combination with a heat source) and providing draft for a
fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because the conversion of the weak double bond in molecula ...

fire
. Fans also have several applications in the industries. Some fans directly cool the machine and process, and may be indirectly used for cooling in the case of industrial heat exchangers. While fans are often used to cool people, they do not cool air (electric fans may warm it slightly due to the heat produced by their motors), but work by
evaporative cooling An evaporative cooler (also evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation Evaporation is a type of that occurs on the of a as it changes int ...
of
sweat Perspiration, also known as sweating, is the production of fluids secreted by the sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin Skin is the layer of usually soft, fle ...

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

convection
into the surrounding air, due to the airflow from the fans. Thus, fans may become ineffective at cooling the body if the surrounding air is near body temperature and contains high humidity.


History

The
punkah A punkah, also pankha (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, North India. Hind ...
fan was used in
India India, officially the Republic of India (Hindi Hindi (Devanagari: , हिंदी, ISO 15919, ISO: ), or more precisely Modern Standard Hindi (Devanagari: , ISO 15919, ISO: ), is an Indo-Aryan language spoken chiefly in Hindi Belt, ...

India
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 ''rāj'', literally, "rule" in Sanskrit Sanskrit (, attributively , ''saṃskṛta-'', nominalization, nominally , ''saṃskṛtam'') is a classical language of South Asia belonging to the Indo-Aryan languages, ...

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
punkawallah
. For purposes of
air conditioning Air conditioning (also A/C, air conditioner) is the process of removing heat and controlling the humidity Humidity is the concentration of water vapour (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 ...
, the
Han Dynasty#REDIRECT Han dynasty The Han dynasty () was the second Dynasties in Chinese history, imperial dynasty of China (202 BC – 220 AD), established by the rebel leader Liu Bang and ruled by the House of Liu. Preceded by the short-lived Qin dynas ...

Han Dynasty
craftsman and engineer
Ding HuanDing Huan () was a Chinese craftsman, and inventor who lived in the first century BC during the Han dynasty The Han dynasty () was the second Dynasties in Chinese history, imperial dynasty of China (202 BC – 220 AD), established by the rebel ...
(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 (, ; ), or Tang Empire, was an imperial dynasty of China that ruled from 618 to 907, with an interregnum An interregnum (plural interregna or interregnums) is a period of discontinuity or "gap" in a government, organiza ...
(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 Emperor Taizu of Song (21 March 927 – 14 November 976), personal name Zhao Kua ...
(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 Julian_calendar">nowiki/>Julian_calendar.html" ;"title="Julian_calendar.html" ;"title="nowiki/>Julian calendar">nowiki/>Julian calendar">Julian_calendar.h ...

Otto von Guericke
,
Robert Hooke Robert Hooke FRS FRS may also refer to: Government and politics * Facility Registry System, a centrally managed Environmental Protection Agency database that identifies places of environmental interest in the United States * Family Resources ...
and
Robert Boyle Robert Boyle (; 25 January 1627 – 31 December 1691) was an Anglo-Irish natural philosopher, chemist, physicist, and inventor. Boyle is largely regarded today as the first modern chemist, and therefore one of the founders of modern che ...

Robert Boyle
, established the basic principles of vacuum and airflow. The English architect Sir
Christopher Wren Sir Christopher Wren PRS FRS FRS may also refer to: Government and politics * Facility Registry System, a centrally managed Environmental Protection Agency database that identifies places of environmental interest in the United States * Fa ...

Christopher Wren
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 of the United Kingdom, House of Commons and the House of Lords, the two houses of the Parliament of the United Kingdom. Informally known as the Houses of Parliame ...

Houses of Parliament
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 people, German Renaissance humanism, Humanist scholar, mineralogy, mineralogist and metallurgy, metallurgist. Born in the small town of Gl ...

Georg Agricola
(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 The Royal Society, formally The Royal Society of London for Impr ...

John Theophilus Desaguliers
, 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 A civil engineer is a person who practices civil engineering Civil engineering is a Regulation and licensure in engineering, professional engineering discip ...

John Smeaton
, 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 Northumberland Coalfield, Northern Coalfield in the first half ...
installed reciprocating air pumps in the mines in the North of
England England is a Countries of the United Kingdom, 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 of England and the Celtic Sea to the southwest. E ...

England
. 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 father ...
, was made operational in the Gelly Gaer
Colliery Coal mining is the process of from the ground. Coal is valued for its and since the 1880s has been widely used to generate electricity. and industries use coal as a fuel for extraction of iron from and for cement production. In the and ...
of
South Wales South Wales ( cy, De Cymru) is a loosely defined region of Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Iri ...

South Wales
. The model was exhibited at the
Great Exhibition opens the Great Exhibition in The Crystal Palace The Crystal Palace was a cast iron and plate glass structure, originally built in Hyde Park, London, Hyde Park, London, to house the Great Exhibition of 1851. The exhibition took place from 1 M ...
of 1851. Also in 1851
David Boswell Reid Prof David Boswell Reid MD FRSE Fellowship of the Royal Society of Edinburgh (FRSE) is an award granted to individuals that the Royal Society of Edinburgh, Scotland's national academy of science and Literature, letters, judged to be "eminent ...

David Boswell Reid
, a Scottish doctor, installed four steam-powered fans in the ceiling of
St George's Hospital St George's Hospital is a teaching hospital in Tooting Tooting is a district of South London, England, forming part of the London Borough of Wandsworth and partly in the London Borough of Merton. It is located south south-west of Charing Cro ...
in
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, tenth largest English district by population, and its ...

Liverpool
, 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, ...

James Nasmyth
, Frenchman Theophile Guibal and J. R. Waddle.


Electrical

Between 1882 and 1886 Schuyler Wheeler invented a fan powered by electricity. It was commercially marketed by the American firm Crocker & Curtis electric motor company. In 1885 a desktop electric fan was commercially available by Stout, Meadowcraft & Co. in New York. In 1882, Philip Diehl developed the world's first electric
ceiling fan A ceiling fan is a mechanical fan mounted on the ceiling of a room or space, usually electrically powered, that uses hub-mounted rotating A rotation is a circular movement of an object around a center (or point) of rotation. The plane ...

ceiling 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 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
air conditioning Air conditioning (also A/C, air conditioner) is the process of removing heat and controlling the humidity Humidity is the concentration of water vapour (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 ...
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 A wall is a structure and a surface that defines an area; carries a load; provides security Security is freedom from, or resilience against, potential Potential generally refers to a currently unrealize ...
, wall, roof, chimney, etc. Most electronic systems such as
computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer program, programs. These ...

computer
s 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 A chart of wind chill values for given air temperatures and wind speeds 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 low ...

wind chill
by increasing the
heat transfer coefficient The heat transfer coefficient or film coefficient, or film effectiveness, in thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and th ...
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 may refer to: Computing * Parallel algorithm In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their a ...
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 heat rejection device that rejects waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Cooling towers may either use the evaporation of water to remove process heat and cool the worki ...

cooling towers
. 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 A wire is a single usually cylindrical A cylinder (from ) has traditionally been a Solid geometry, three-dimensional solid, one of the most basic of curvilinear geometric shapes. Geometrically, it can be considered as a Prism (geometry), p ...

wire
s, motor, blade
guard Guard or guards may refer to: Professional occupations * Bodyguard, who protects an individual from personal assault * Crossing guard, who stops traffic so pedestrians can cross the street * Lifeguard, who rescues people from drowning * Prison gua ...
, motor housing,
oscillator Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of Mechanical equilibrium, equilibrium) or between two or more different states. The term ''vibration'' is precisely used to describe ...

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 mechanical fan mounted on the ceiling of a room or space, usually electrically powered, that uses hub-mounted rotating A rotation is a circular movement of an object around a center (or point) of rotation. The plane ...

Ceiling fan
: 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 wheeled motor vehicle A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled vehicle, commonly wheeled, that does not operate on Track (rail transport), rails (such as trains o ...

automobile
s, a mechanical fan provides
engine cooling An engine or motor is a machine designed to convert one form of energy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural ...
and prevents the engine from overheating by blowing or drawing air through a
coolant A coolant is a substance, typically liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics con ...

coolant
-filled
radiator Radiators are heat exchanger A heat exchanger is a system used to transfer heat between two or more fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or externa ...

radiator
. The fan may be driven with a belt and pulley off the
engine An engine or motor is a machine A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular machine that uses Power (physics), power to apply For ...
's
crankshaft A crankshaft is a shaft Shaft may refer to: Rotating machine elements * Shaft (mechanical engineering), a rotating machine element used to transmit power * Line shaft, a power transmission system * Drive shaft, a shaft for transferring torque ...

crankshaft
or an electric motor switched on or off by a
thermostat A thermostat is a regulating device component which senses the temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can be seen ...

thermostat
ic
switch In electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics The field of electronics is a branch of p ...

switch
. *
Computer fan (sometimes as a set, or mixed with other fan sizes) A computer fan is any fan (machine), fan inside, or attached to, a computer case A computer is a machine A machine is a man-made device that uses power to apply forces and control ...
for cooling electrical components and in
laptop cooler
laptop cooler
s * Fans inside
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 radio receiver or electric guitar pickup (music technology), pickup to a level that is high enough for ...
s help to draw heat away from the electrical components. *
Variable pitch fan Although variable pitch fans are used in some industrial applications, the focus of this article is on their use in turbofan engines The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft engine, aircraft p ...
: 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. File:Ventilador Electrico Piso.jpg, alt=Small box fan with wide feet for stability, Household electric "box" fan with a propeller-style blade File:YangonTrainFan.webm, A multi-directional ceiling fan in . File:Joy Axial Variable Pitch Fan.JPG, 80 hp variable-pitch supply fan


Centrifugal

Often called a "squirrel cage" (because of its general similarity in appearance to
exercise wheels
exercise wheels
for pet rodents) or "scroll fan", the centrifugal fan has a moving component (called an
impeller An impeller or impellor is a wikt:rotor#English, 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 ...

impeller
) 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:
, 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 In Newtonian mechanics, the centrifugal force is an inertial force A fictitious force (also called a pseudo force, d'Alembert force, or inertial force) is a force that appears to act on a mass whose motion is described using a non-inertial ref ...
). The impeller rotates, causing air to enter the fan near the shaft and move
perpendicular In elementary geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . It is concerned with properties of space that are related with distance, shape, size, and relativ ...

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 A leaf blower, commonly known as a blower, is a gardening tool that propels air out of a nozzle to move debris such as leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant plant stem, stem, usually born ...

leaf blower
s,
blowdryer A hair dryer, hairdryer or blow dryer is an electromechanical In engineering Engineering is the use of scientific method, scientific principles to design and build machines, structures, and other items, including bridges, tunnels, road ...
s, air mattress inflators,
inflatable structure s are the most common type of inflatable. An inflatable is an object that can be inflated with a gas, usually with air, but hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a stand ...
s,
climate control Heating, ventilation, and air conditioning (HVAC) is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical eng ...
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


Cross-flow fan

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 File:Control circuit in household HVAC unit.jpg, The control circuit in a household HVAC installation. The wires connecting to the blue terminal block on the upper-right of the board lead to the thermostat. The fan enclosure is directly behind th ...
(HVAC), especially in ductless split air conditioners. The fan is usually long concerning the diameter, so the flow remains approximately two-dimensional away from the ends. The cross-flow fan uses an
impeller An impeller or impellor is a wikt:rotor#English, 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 ...

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. 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 Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', ...

turbine
s (pressure decrease). Since the flow both enters and exits the impeller radially, the crossflow fan is well suited for aircraft applications. Due to the two-dimensional nature of the flow, the fan readily integrates 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 An airfoil (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the Unit ...

leading edge
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. Principles of operation A cr ...
. This design creates lift by deflecting the wake downward due to the rotational direction of the fan, causing 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. In this design, the crossflow fan is placed near the trailing edge of a thick wing and draws the air of the wing's suction (top) surface. By doing this, the propulsive wing is nearly stall-free, even at extremely high angles of attack, producing very high lift. The external links section provides links to these concepts. 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, presumably because the fan blades fight the flow of air on one side of the rotation, unlike typical centrifugal fans. Cross-flow fans are often used in ductless air conditioners, air doors, in some types of
laptop cooler
laptop cooler
s, in automobile ventilation systems, and for cooling in medium-sized equipment such as photocopiers.


Uncommon types


Bellows

Bellows are also used to move air, although not generally considered fans. A hand-operated bellows is essentially a bag with a nozzle and handles, which can be filled with air by one movement, and the air expelled by another. Typically it would comprise two rigid flat surfaces hinged at one end, where a nozzle is fitted, and with handles at the other. The sides of the surfaces are joined by a flexible and air-proof material such as leather; the surfaces and joining material comprise a bag sealed everywhere but at the nozzle. (The joining material typically has a characteristic pleated construction that is so common that similar expanding fabric arrangements not used for moving air, such as on a folding camera, are called Bellows (photography), bellows.) Separating 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 having to come from the nozzle, which may be close to a fire. Bellows produce a directed pressurized stream of air; the airflow volume is typically low with moderate pressure. They are an older technology, used mainly to produce a strong and directed airflow, unlike non-electric bladed mechanical fans, before the introduction of electricity. * A single-acting bellows will only produce airflow during the exhaust stroke. * A double-acting bellows is a pair of bellows capable of blowing out air from one while inhaling air into the other, but airflow still temporarily ceases when the stroke direction is reversed. * Combining multiple bellows at third-cycle or quarter-cycle arrangements on a crank arm allows for nearly continuous airflow from several bellows at once; each is in a different phase of inhaling and exhausting during the cycle.


Coandă effect

The Dyson Air Multiplier fans, and the Imperial C2000 series Kitchen hood, range hood fans, have no exposed fan blades or other visibly moving parts except their oscillating and tilting head. The airflow is generated using the Coandă effect; a small quantity of air from a high-pressure-bladed impeller fan, contained in the base rather than exposed, drives a large airmass via a low-pressure area created by the airfoil. The US Patent & Trademark Office initially ruled that Dyson's patent was not an improvement on the Toshiba patent on a nearly identical bladeless desktop fan granted in 1981. 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 described in this article 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.


Convective

Differences in air temperature will affect the density of air and can be used to induce air circulation through the mere act of heating or cooling an air mass. This effect is so subtle and works at such low air pressures that it does not appear to fit the definition of fan technology. However, before the development of electricity, convective airflow was the primary method of inducing airflow in living spaces. Old fashioned oil and coal furnaces were not electric and operated simply on the principle of convection to move the warm air. Very large volume air ducts were sloped upwards away from the top of the furnace towards floor and wall registers above the furnace. Cool air was returned through similar large ducts leading to the bottom of the furnace. Older houses from before electrification often had open duct grilles leading from the ceiling of a lower level to the floor of an upper level, to allow convective airflow to slowly raise the building from one floor to the next. Outhouses commonly rely on a simple enclosed air channel in a corner of the structure to exhaust offensive odors. Exposed to sunlight, the channel is warmed and slow convective air current is vented out the top of the building, while fresh air enters the pit through the seat hole.


Electrostatic

An electrostatic fluid accelerator propels airflow by inducing motion in airborne charged particles. A high voltage electric field (commonly 25,000 to 50,000 volts) formed between exposed charged anode and cathode surfaces is capable of inducing airflow through a principle referred to as ionic wind. The airflow pressure is typically very low but the air volume can be large. However, a sufficiently high voltage potential can also cause the formation of ozone and nitrogen oxides, which are reactive and irritating to mucous membranes.


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. 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 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. 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 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. In machines with a rotating part, the fan is often connected to it rather than being powered separately. This is commonly seen in motor vehicles with
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and ...

internal combustion engine
s, large cooling systems, locomotives, and winnowing machines, where the fan is connected to the drive shaft or through a belt and pulleys. Another common configuration is a dual-shaft motor, where one end of the shaft drives a mechanism, while the other has a fan mounted on it to cool the motor itself. Window air conditioners commonly use a dual-shaft fan to operate separate fans for the interior and exterior parts of the device. Where electrical power or rotating parts are not readily available, fans may be driven by other methods. High-pressure gases such as steam can be used to drive a small
turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', ...

turbine
, and high-pressure liquids can be used to drive a pelton wheel, 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 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 engines 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 powered fan

Electric fans used for ventilation may be powered by Photovoltaic module, solar panels instead of mains current. This is an attractive option because once the capital costs of the solar panel have been covered, the resulting electricity is free. 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, solar panel and is supplied with appropriate brackets, Power cable, cables, and Electrical connector, connectors. It can be used to ventilate up to of area and can move air at up to . Because of the wide availability of 12 V brushless DC electric motors and the convenience of wiring such a low voltage, such fans usually operate on 12 volts. 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.


See also


References


External links

* {{DEFAULTSORT:Mechanical Fan Ventilation fans, Turbomachinery Cooling technology Ventilation Heating, ventilation, and air conditioning Mechanical engineering Chemical engineering Gas compressors Turbines Thermodynamics Fluid dynamics Aerodynamics