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Fan (mechanical)

A mechanical fan is an electrically powered device used to produce an airflow for the purpose of creature comfort (particularly in the heat), ventilation, exhaust, or any other gaseous transport.

Mechanically, a fan can be any revolving vane or vanes used for producing currents of air. Fans produce air flows with high volume and low pressure, as opposed to a gas compressor which produces 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, cooling systems, personal comfort (e.g., an electric table fan), ventilation (e.g., an exhaust fan), winnowing (e.g., separating chaff of cereal grains), removing dust (e.g. sucking as in a vacuum cleaner), drying (usually in addition to 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 1800s 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..

History

The first recorded mechanical fan was the punkah fan used in the Middle East in the early 1800s. It had a canvas covered frame that was suspended from the ceiling. Servants, known as punkah wallahs, pulled a rope connected to the frame to move the fan back and forth.

The Industrial Revolution in the late 1800s introduced belt-driven fans powered by factory waterwheels. 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 Alexander Sablukov 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 1800s and early 1900s for the public, the personal electrical fan was introduced. Between 1882 and 1886, Dr. Schuyler Skaats Wheeler developed the two-bladed desk fan, a type of personal electric fan. It was commercially marketed by the American firm Crocker & Curtis electric motor company. In 1882, Philip Diehl introduced the electric ceiling fan. Diehl is considered the father of the modern electric fan. In the late 1800s, electric fans were used only in commercial establishments or in well-to-do households. Heat-convection fans fueled by alcohol, oil, or kerosene were common around the turn of the 20th century.

The first American made fans, made from around the late 1890s to the early 1920s were very stylish. They had brass blades, a lot 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 was designed. Before this fan, called the Silver Swan, most household fans were fairly plain. In the 1950s, fans were manufactured in colors that were bright and eye catching. Central air conditioning in the 1960s brought an end to the golden age of the electric fan. 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). 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 cooling in air-conditioning systems, and in automotive engines, where they are driven by belts or by direct motor. Fans create a wind chill but do not lower temperatures directly.

There are three main types of fans used for moving air, axial, centrifugal (also called radial) and cross flow (also called tangential).

Axial fans

The axial-flow fans have blades that force air to move parallel to the shaft about which the blades rotate. Axial fans blow air across 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 motions 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.

Electro-mechanical fans, among collectors, are rated according to their condition, size, age, and number of blades. Four-blade designs are the most common. Five-blade or six-blade designs are rare. The materials from which the components are made, such as brass, are important factors in fan desirability.

  • Ceiling fan - A fan suspended from the ceiling of a room is a ceiling fan.
  • In automobiles, a mechanical fan, driven with a belt and pulley off the engine's crankshaft, or an electric fan switched on/off by a thermo switch is used to blow or suck air through a coolant filled radiator, to prevent the engine from overheating.
  • Computer fan
  • Variable Pitch Fan A variable pitch fan is used where precise control of static pressure within supply ducts is required. The fan wheel will spin at a constant RPM (1780 in this case). 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 fan

Often called a "squirrel cage" (due to 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, air mattress inflators, and various industrial purposes. They are typically noisier than comparable axial fans.

Cross flow fan

A cross flow fan, is a centrifugal fan in which the air flows through the fan, rather than through an inlet. The rotor of a cross flow fan is covered to create a pressure differential. When used in household fans, cross flow fans have a smaller opening on one side and a larger opening on the other. 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. Cross flow fans are noisier than ordinary centrifugal fans presumedly because the fan blades fight the flow of air on one side of the rotation unlike normal squirrel cage fans. Cross flow fans are often used in air conditioners, automobile ventilation systems, and for cooling in medium-sized equipment such as photocopiers. The action of a fan or blower causes pressures slightly above atmospheric, which are called plenums.

Fan motor

A stand alone 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, 3-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 which already have a motor, the fan is often connected to this rather than being powered independently. This is commonly seen in cars, boats, large cooling systems and winnowing machines, where the fan is connected either directly to the driveshaft 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.

Solar powered fan

Electric fans used for ventilation may be powered by 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. In addition, electricity is always available when the sun is shining and the fan needs to run.

A typical example uses a detached 10 watt, 12x12 inch (30x30 cm) solar panel and is supplied with appropriate brackets, cables, and connectors. It can be used to ventilate up to 1250 square feet (100 m²) of area and can move air at up to 800 cubic feet per minute (400 L/s). 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 sun light and then connected to the fan mounted as far as 20 to 25 feet (6 to 7 m) away. Other permanently-mounted and small portable fans include an integrated (non-detachable) solar panel.

See also

References

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