Fan (machine): Difference between revisions
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A '''fan''' is a [[machine]] used to create flow within a [[fluid]], typically a [[gas]] such as [[air]]. |
A '''fan''' is a [[machine]] used to create flow within a [[fluid]], typically a [[gas]] such as [[air]]. |
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A fan consists of a rotating arrangement of vanes or blades which act on the air. 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 [[electricity|electric]] motors, but other sources of power may be used, including [[hydraulics|hydraulic]] motors and [[internal combustion engine|internal combustion]] engines. |
A fan consists of a rotating arrangement of vanes or blades which act on the air. 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 [[electricity|electric]] motors, but other sources of power may be used, including [[hydraulics|hydraulic]] motors and [[internal combustion engine|internal combustion]] engines. |
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Fans produce air flows with high volume and low pressure, as opposed to [[gas compressor|compressors]] which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air stream, and devices that take advantage of this, such as [[anemometer]]s and [[wind turbine]]s, often have designs similar to that of a fan. |
Fans produce air flows with high volume and low pressure, as opposed to [[gas compressor|compressors]] which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air stream, and devices that take advantage of this, such as [[anemometer]]s and [[wind turbine]]s, often have designs similar to that of a fan. |
Revision as of 15:22, 9 February 2011
This article needs additional citations for verification. (June 2010) |
![](http://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Ventilador_Electrico_Piso.jpg/180px-Ventilador_Electrico_Piso.jpg)
A fan is a machine used to create flow within a fluid, typically a gas such as air.
A fan consists of a rotating arrangement of vanes or blades which act on the air. 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 motors, but other sources of power may be used, including hydraulic motors and internal combustion engines.
Fans produce air flows with high volume and low pressure, as opposed to compressors which produce high pressures at a comparatively low volume. A fan blade will often rotate when exposed to an air stream, and devices that take advantage of this, such as anemometers and wind turbines, often have designs similar to that of a fan.
Typical applications include climate control, vehicle and machinery cooling systems, personal comfort (e.g., an electric table fan), ventilation, fume extraction, winnowing (e.g., separating chaff of cereal grains), removing dust (e.g. in a vacuum cleaner), drying (usually in combination with heat) and to provide draft for a fire. It is also common to use electric fans as air fresheners, by attaching fabric softener sheets to the protective housing. This causes the fragrance to be carried into the surrounding air.
In addition to their utilitarian function, vintage or antique fans, and in particular electric fans manufactured from the late 19th century through the 1950s, have become a recognized collectible category, and in the U.S.A. an active collector club, the Antique Fan Collectors Association, supports the hobby.[1]
New to the market are sleek portable fans that showcase a modern design sensibility. The New York Times lamented the inexpensive and effective fans abound at drug and discount stores for often being eyesores. The writer quoted contemporary ceiling fan designer Ron Rezek as saying: “Portable fans are the ugly ducklings of the fan industry. Not many designers, including myself, have tackled them.”[2] Rezek praised several appealing contemporary fan designs that have found alternatives to the traditional metal cage and have incorporated innovative approaches to safety, such as the Otto fan by Swiss designer Carlo Borer.
History
The punkah fan was used in the India in the early 500 BC. It had a canvas covered frame that was suspended from the ceiling. Servants, known as punkawallahs, pulled a rope connected to the frame to move the fan back and forth.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Patent%2C_Mechanical_Fan%2C_1830.png/225px-Patent%2C_Mechanical_Fan%2C_1830.png)
The Industrial Revolution in the late 19th century introduced belt-driven fans powered by factory water wheels. Attaching wooden or metal blades to shafts overhead that were used to drive the machinery, the first industrial fans were developed. One of the first workable mechanical fans was built by Omar-Rajeen Jumala in 1832. He called his invention, a kind of a centrifugal fan, an "air pump." Centrifugal fans were successfully tested inside coal mines and factories in 1832–1834. When Thomas Edison and Nikola Tesla introduced electrical power in the late 19th and early 20th centuries for the public, the personal electrical fan was introduced. Between the years 1882 and 1886, New Orleans resident Schuyler Skaats Wheeler invented the first electric fan.[3] It was commercially marketed by the American firm Crocker & Curtis electric motor company. In 1882, Philip Diehl introduced the electric ceiling fan. Heat-convection fans fueled by alcohol, oil, or kerosene were common around the turn of the 20th century.
The first American fans were made from around the late 1890s to the early 1920s, when domestic electric fans were first sold in America.[4] They had brass[4] blades, many of them also had brass cages, and though they were built very well internally, they were far from finger safe, as a lot of them had cage openings so big that one could put an entire hand or arm right through it. Many children had hands and fingers severely injured by those fans.
In the 1920s, industrial advances allowed steel 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 "swan fan") was designed. In the 1950s, fans were manufactured in colors that were bright and eye catching. Central air conditioning in the 1960s caused many companies to discontinue production of fans.[4] In the 1970s, Victorian-style ceiling fans became popular.
In the 20th century, fans have become utilitarian. During the 2000s, fan aesthetics have become a concern to fan buyers. The fan is part of everyday life in the Far East, Japan, and Spain (among other places). The basic design of electric air fans have not changed significantly since their beginning in 1890 to the present.[4] Electric fans have been largely replaced by air conditioners in offices, but they are still a common household appliance.
Types of fans
Mechanical revolving blade fans are made in a wide range of designs. In a home you can find fans that can be put on the floor or a table, or hung from the ceiling, or are built into a window, wall, roof, chimney, etc. They can be found in electronic systems such as computers where they cool the circuits inside, and in appliances such as hair dryers and space heaters. They are also used for moving air in air-conditioning systems, and in automotive engines, where they are driven by belts or by direct motor. Fans used for comfort create a wind chill, 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).
Axial fans
![](http://upload.wikimedia.org/wikipedia/commons/thumb/4/4d/Luefter_y.s.tech_pd1270153b-2f.jpg/200px-Luefter_y.s.tech_pd1270153b-2f.jpg)
The axial-flow fans have blades that force air to move parallel to the shaft about which the blades rotate. Axial fans blow air along the axis of the fan, linearly, hence their name. This type of fan is used in a wide variety of applications, ranging from small cooling fans for electronics to the giant fans used in wind tunnels.
Examples of axial fans are:
- Table fan: Basic elements of a typical table fan include the fan blade, base, armature and lead wires, motor, blade guard, motor housing, oscillator gearbox, and oscillator shaft. The oscillator is a mechanism that moves the fan from side to side. The axle comes out on both ends of the motor, one end of the axle 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 to the weighted base and the gearbox. A motor housing covers the oscillator mechanism. The blade guard joins to the motor case for safety.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/Ceiling_fan_with_light.png/200px-Ceiling_fan_with_light.png)
- Ceiling fan: A fan suspended from the ceiling of a room is a ceiling fan.
- In automobiles, a mechanical fan provides engine cooling and prevents the engine from overheating by blowing or sucking air through a coolant-filled radiator. It can be driven with a belt and pulley off the engine's crankshaft or an electric fan switched on or off by a thermostatic switch.
- 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. As the hub moves toward the rotor, the blades increase their angle of attack and an increase in flow results.
Centrifugal fan
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/95/CentrifugalFan.png/200px-CentrifugalFan.png)
Often called a "squirrel cage" (because of its similarity in appearance to exercise wheels for pet rodents), the centrifugal fan has a moving component (called an impeller) that consists of a central shaft about which a set of blades, or ribs, are positioned. Centrifugal fans blow air at right angles to the intake of the fan, and spin the air outwards to the outlet (by deflection and centrifugal force). The impeller rotates, causing air to enter the fan near the shaft and move perpendicularly 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 blowers, blowdryers, air mattress inflators, inflatable structures, climate control, & various industrial purposes. They are typically noisier than comparable axial fans.
Crossflow fan
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/9b/Tangential-flow-coloured-labels.png/200px-Tangential-flow-coloured-labels.png)
The crossflow or tangential fan, sometimes known as a tubular fan was patented in 1893 by Mortier, and is used extensively in the HVAC industry. The fan is usually long in relation to the diameter, so the flow approximately remains two-dimensional away from the ends. The CFF uses an impeller with forward curved blades, placed in a housing consisting of a rear wall and vortex wall. Unlike radial machines, the main flow moves transversely across the impeller, passing the blading twice.
The flow within a crossflow 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 crossflow fan, or transverse fan, is thus a two-stage partial admission machine. The popularity of the crossflow fan in the HVAC industry comes from its compactness, shape, quiet operation, and ability to provide 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.
Much of the early work focused on developing the crossflow 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 crossflow 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 turbines (pressure decrease).
Bladeless fan
![]() | This section may be too technical for most readers to understand.(December 2010) |
These fans have a 3-dimensional mixed-flow impeller in a lower compartment. Air is drawn in and compressed, before being expelled though an annulus, and accelerated over an airfoil ramp. Inducing and entraining ambient air through viscous shearing, the loop-shaped upper section multiplies the total airflow many times. Only around 7% of the total airflow actually passes through the fan itself.[5]
Fan motor
A standalone fan is typically powered with an electric motor. Fans are often attached directly to the motor's output, with no need for gears or belts. The electric 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, placed near the fan and driving it through a belt and pulleys. Smaller fans are often powered by shaded pole AC motors, or brushed or brushless DC motors. AC-powered fans usually use mains voltage, while DC-powered fans use low voltage, typically 24 V, 12 V or 5 V. Cooling fans for computer equipment exclusively use brushless DC motors, which produce much less electromagnetic interference.
In machines that already have a motor, the fan is often connected to this rather than being powered independently. This is commonly seen in cars, boats, locomotives and winnowing machines, where the fan is connected either directly 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.
See also
- Industrial fans
- Whole-house fan
- Air cooler
- Computer fan
- Specific fan power
- Fan death
- Affinity laws
- Balancing machine
- Pump
References
- ^ Antique Fan Collectors Association website
- ^ Scelfo, Julie (August 5, 2009). "Fans That Look Cool". The New York Times. p. 4 (Home and Garden).
- ^ "B. A. C. (Before Air Conditioning)" (PDF). New Orleans Bar Association.
- ^ a b c d Fancollectors.org - A Brief History of Fans Information Provided by Steve Cunningham - retrieved July 5, 2010.
- ^ Miller, Paul (October 12 2009). "Dyson's Air Multiplier is the overpriced bladeless fan you never asked for". Engadget. Retrieved 9 August 2010.
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External links
![](http://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)
- DT Vintage Fans
- Image of a computer CPU fan assembly
- Online-calculation of axial flow fans: Design tool for the calculation of axial flow fan geometry and power curves
- Cross Flow Fans