fan, device for agitating air or gases or moving them from one location to another. Mechanical fans with revolving blades are used for ventilation, in manufacturing, in winnowing grain, to remove dust, cuttings, or other waste, or to provide draft for a fire. They are also used to move air for cooling purposes, as in automotive engines and air-conditioning systems, and are driven by belts or by direct motor. The axial-flow fan (e.g., an electric table fan) has blades that force air to move parallel to the shaft about which the blades rotate. The centrifugal fan has a moving component, called an impeller, that consists of a central shaft about which a set of blades form a spiral pattern. When the impeller rotates, air that enters the fan near the shaft is moved away perpendicularly from the shaft and out of an opening in the scroll-shaped fan casing. As a light, flat instrument manipulated by hand to cool the body or ward off insects, the fan is of tropical origin and probably stems from the primitive use of palm or other leaves. The long-handled, disk-shaped fan carried by attendants was from ancient times associated with regal and religious ceremonies. In China an early form of the hand fan was a row of feathers mounted in the end of a handle; in Greece linen was often stretched over a leaf-shaped frame; and in Rome wooden fans, gilded and painted, were used. In Europe during the Middle Ages the fan virtually disappeared until the 13th and 14th cent., when fans from the Middle East were brought back by Crusaders and became fashionable for the wealthy. After 1500 the fan became generally popular; flag fans, disk-shaped fans, and tuft fans of ostrich plumes or peacock feathers, with handles of carved ivory or gold set with jewels, were common in women's wardrobes. In c.1600 the folding fan, developed in medieval Japan and introduced into Europe by way of China, became popular. The slats, of ivory, bone, mica, mother-of-pearl, or tortoiseshell, were delicately carved and covered with paper or fabric. The fan reached a high degree of artistry, especially in France, in the 17th and 18th cent. Delicately folded fans of lace, silk, or parchment were decorated with original designs and paintings by contemporary artists. The management of the fan became a highly regarded feminine art. The function and employment of the fan reached its high point of social significance in Japan.
fan
Rigid or folding handheld device used for cooling, air circulation, or ceremony or as a sartorial accessory throughout the world from ancient times. As evidenced by Egyptian reliefs, early fans were of the rigid type, with a handle or stick attached to a rigid leaf or to feathers. In China, the folding fan came into fashion during the Ming dynasty (1368–1644); much significance came to be attached to the fan in East Asia, and many great Chinese painters devoted their talents to fan decoration. Portuguese traders in the 15th century brought fans to Europe from China and Japan. Through the 19th century in the West, fan decoration and size varied with European fashion.
fan
A device that uses motor-driven blades to circulate the air in a computer or other electronic system. Today's CPUs run extremely hot, and large computer cabinets use two and three fans to reduce temperature. See FanCard.
fan Engineeringa. any device for creating a current of air by movement of a surface or number of surfaces, esp a rotating device consisting of a number of blades attached to a central hub
b. a machine that rotates such a device
fan [
fan]
(agriculture)
A mechanical device used for winnowing grain.
(biology)
Any structure, such as a leaf or the tail of a bird, resembling an open fan.
(electromagnetism)
Volume of space periodically energized by a radar beam (or beams) repeatedly traversing an established pattern.
(geology)
A gently sloping, fan-shaped feature usually found near the lower termination of a canyon.
(mechanical engineering)
A device, usually consisting of a rotating paddle wheel or an airscrew, with or without a casing, for producing currents in order to circulate, exhaust, or deliver large volumes of air or gas.
A vane to keep the sails of a windmill facing the direction of the wind.
Fan A fan moves gases by producing a low compression ratio, as in ventilation and pneumatic conveying of materials. The increase in density of the gas in passing through a fan is generally negligible; the pressure increase or head is usually measured in inches of water.
Blowers are fans that operate where the resistance to gas flow is predominantly downstream of the fan. Exhausters are fans that operate where the flow resistance is mainly upstream of the fan.
Fans are further classified as centrifugal or axial (see illustration). The housing provides an inlet and an outlet and confines the flow to the region swept out by the rotating impeller. The impeller imparts velocity to the gas, and this velocity changes to a pressure differential under the influence of the housing and ducts connected to inlet and outlet.
Fan types
fan
symbol of coquetry. [Folklore: Jobes, 370]
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