Fan (machine)

A fan is a powered machine that creates airflow. A fan consists of rotating vanes or blades, generally made of wood, plastic, or metal, which act on the air. The rotating assembly of blades and hub is known as an impeller, rotor, or runner. Usually, it is contained within some form of housing, or case. This housing will allow air to past through as well as directing the airflow, or increasing 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, handcranks, and internal combustion engines.
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 compressors 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 anemometers and wind turbines, often have designs similar to that of a fan.
Typical applications include climate control and personal thermal comfort, vehicle engine cooling systems, machinery cooling systems, ventilation, fume extraction, winnowing, removing dust, drying and providing draft for a fire. 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. Instead, they work by evaporative cooling of sweat and increased heat convection 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

Fans made with leaves were prevalent in ancient Egypt and India. In ancient India, they were handheld fans made from bamboo strips or other plant fiber, that could be rotated or fanned to move air. During 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.
For purposes of air conditioning, the Han dynasty craftsman and engineer Ding Huan invented a manually operated rotary fan with seven wheels that measured 3 m in diameter; in the 8th century, during the Tang dynasty, 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.
During the Heian period in Japan, fans adapted the role of symbolizing social class as well as a mechanical role. The tessen, a Japanese fan used in Feudal times, was a dangerous weapon hidden in plain sight in the shape of a regular fan, a weapon used by samurais when katanas were not ideal.
In the 17th century, the experiments of scientists, including Otto von Guericke, Robert Hooke, and Robert Boyle, established the basic principles of vacuum and airflow. The English architect Sir Christopher Wren applied an early ventilation system in the Houses of Parliament that used bellows to circulate air. Wren's design was 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.
John Theophilus Desaguliers, a British engineer, demonstrated the successful use of a fan system to draw out stagnant air from coal mines in 1727—ventilation was essential in coal mines to prevent asphyxiation—and soon afterward he installed a similar apparatus in Parliament. The civil engineer John Smeaton, and later John Buddle, installed reciprocating air pumps in the mines in the North of England, though the machinery was liable to breaking down.

Steam

In 1849 a 6m radius steam-driven fan, designed by William Brunton, was made operational in the Gelly Gaer Colliery of South Wales. The model was exhibited at the Great Exhibition of 1851. Also in 1851 David Boswell Reid, a Scottish doctor installed four steam-powered fans in the ceiling of St George's Hospital in 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, 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 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 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 were eye-catching. Ceiling fans are extremely popular in South Asian countries such as India, where they provide cost-effective cooling in hot climates.
Window and central air conditioning in the 1960s caused many companies to discontinue production of fans, 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 popular again as both decorative and energy-efficient.
In 1998 William Fairbank and Walter K. Boyd invented the high-volume low-speed ceiling fan, designed to reduce energy consumption by using long fan blades rotating at low speed to move a relatively large volume of air.

Social implications

Before powered fans were widely accessible, their use related to the social divide between social classes. In Britain and China, they were initially only installed in the buildings of Parliament and in noble homes. In Ancient Egypt, servants were required to fan Pharaohs and important figures.
In parts of the world such as India, where the temperature reaches above, standing and electric box fans are essential in the business world for customer comfort and an efficient work environment. Fans have become solar-powered, energy-efficient, and battery-powered in places with unreliable energy sources.
Typical room electrical fans consume 50 to 100 watts of power, while air-conditioning units use 500 to 4000 watts; fans use less electricity but do not cool the air, simply providing evaporative cooling of sweat. Commercial fans are louder than AC units and can be disruptively loud. According to the U.S. Consumer Product Safety Commission, reported incidents related to box fans include, fire, potential fire, electrocution, electric shock, and electrical hazard. Injuries related to AC units mostly relate to their falling from buildings.

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 and can be built into a window, wall, roof, etc. Tower fans tend to have smaller blades inside. Electronic systems generating significant heat, such as computers, incorporate fans. Appliances such as hair dryers and space heaters also use fans. They move air in air-conditioning systems and in automotive engines. Fans used for comfort inside a room create a wind chill by increasing the heat transfer coefficient but do not lower temperatures directly. Fans used to cool electrical equipment or in engines or other machines cool the equipment directly by exhausting hot air into the cooler environment outside of the machine so that cooler air flows in.
Three main types of fans are used for moving air, axial, centrifugal and cross flow. The American Society of Mechanical Engineers Performance Testing Code 11 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 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. 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 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 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 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 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 impeller, while kitchen extractor fans typically use a six-inch impeller as the room is often bigger. Axial fans with five-inch impellers are also used in larger bathrooms, though they are much less common. Domestic axial extractor fans are unsuitable 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 fan's performance.
Continuous running extractor fans run continuously at a very slow rate, running fast when necessary, for example when a bathroom light is switched on. At working speed, they are just normal extractor fans. They extract typically 5 to 10 l/sec at continuous speed and use little electricity, 1 or 2 watts, for low annual cost. Some have humidity sensors to control trickle operation. They have the advantage of ensuring ventilation and preventing the build-up of humidity. Alternatively, a normal extractor fan may be fitted to operate intermittently at full power for the same purpose. In cold weather they may have noticeably cool the room they are in, or, if the door is open, the house.
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.
A ceiling fan is a fan suspended from the ceiling of a room. Most ceiling fans rotate at relatively low speeds and do not have blade guards because they are inaccessible and unwieldy. Ceiling fans are used in both residential and industrial/commercial settings.
In automobiles, a mechanical or electrically driven fan provides engine cooling and prevents the engine from overheating by blowing or drawing air through a coolant-filled radiator. The fan may be driven with a belt and pulley off the engine's crankshaft or an electric motor switched on or off by a thermostatic switch.
Computer fan for cooling electrical components and in laptop coolers.
Fans inside audio power amplifiers help to draw heat away from the electrical components.
Variable pitch fan: A variable-pitch fan is used to precisely control static pressure within supply ducts. 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.