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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 may direct the airflow, or increase safety by preventing objects from contacting the fan blades. Most fans are powered by , but other sources of power may be used, including , , and internal combustion engines.
Mechanically, a fan can be any revolving , or vanes used for producing air current. Fans produce air flows with high volume and low pressure (although higher than ambient pressure), as opposed to gas compressor 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 and , often have designs similar to that of a fan.
Typical applications include climate control and personal thermal comfort (e.g., an electric table or floor fan), vehicle engine cooling systems (e.g., in front of a radiator), machinery cooling systems (e.g., inside computers and audio power amplifiers), ventilation, fume extraction, winnowing (e.g., separating chaff from cereal grains), removing dust (e.g. sucking as in a vacuum cleaner), drying (usually in combination with a heat source) 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.
For purposes of air conditioning, the Han dynasty craftsman and engineer Ding Huan (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 (618–907), the Chinese applied Hydraulics to rotate the fan wheels for air conditioning, while the rotary fan became even more common during the Song dynasty (960–1279).Needham (1986), Volume 4, Part 2, 99, 134, 151, 233.Day & McNeil (1996), 210.
During the Heian period period (794–1185) in Japan, fans adapted the role of symbolizing social class as well as a mechanical role. The tessen, a Japanese fan used in Feudalism times, was a dangerous weapon hidden in plain sight in the shape of a regular fan, a weapon used by when 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 (1494–1555).Needham, Volume 4, Part 2, 154.
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 in the mines in the North of England, though the machinery was liable to breaking down.
target="_blank" rel="nofollow"> HISTORIC BUILDING ENGINEERING SYSTEMS & EQUIPMENT HEATING & VENTILATION, By Brian Roberts, CIBSE Heritage Group Improvements in the technology were made by James Nasmyth, Frenchman Theophile Guibal and J. R. Waddle.
In 1882, Philip Diehl developed the world's first electric 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 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, 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 popular again as both decorative and energy-efficient.
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.
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.
In South Korea, fans play a part in an old wives' tale. Many older South Korean citizens believe in the unscientific and unsupported myth of fan death due to excessive use of an electric fan; Korean electric fans usually turn off after a few hours to protect from fan death.
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 (266 incidents), potential fire (29 incidents), electrocution (15), electric shock (4 incidents), and electrical hazard (2 incidents). Injuries related to AC units mostly relate to their falling from buildings.
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 (pressure decrease).
Since the flow enters and exits the impeller radially, the crossflow fan has been studied and prototyped for potential aircraft applications. Due to the two-dimensional nature of the flow, the fan can be integrated into a wing for use in both thrust production and boundary-layer control. A configuration that utilizes a crossflow fan located at the wing leading edge is the FanWing design concept initially developed around 1997 and under development by a company of the same name. This design creates lift by deflecting the wake downward due to the rotational direction of the fan, causing a large Magnus effect, similar to a spinning leading-edge cylinder. Another configuration utilizing a crossflow fan for thrust and flow control is the propulsive wing, another experimental concept prototype initially developed in the 1990s and 2000s. In this design, the crossflow fan is placed near the trailing edge of a thick wing and draws the air from 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. However, the fanwing and propulsive wing concepts remain experimental and have only been used for unmanned prototypes.
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. A cross-flow fan has two walls outside the impeller and a thick vortex wall inside. The radial gap decreases in the direction of the impeller rotation. The rear wall has a log-spiral profile, while the vortex stabilizer is a thin horizontal wall with a 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. Cross-flow fans are often used in ductless , , in some types of , in automobile ventilation systems, and for cooling in medium-sized equipment such as .
Air door 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, as described in this article, and is hidden in the base of the display cabinet. HVAC linear slot diffusers also utilize this effect to increase airflow evenly in rooms compared to registers while reducing the energy used by the Air handler Centrifugal fan.
In vehicles, a ducted fan is a method of propulsion in which a fan, [[propeller]] or rotor is surrounded by an aerodynamic duct or shroud which enhances its performance to create aerodynamic thrust or lift to transport the vehicle.
The perceived loudness of fan noise also depends on the frequency distribution of the noise. This depends on the shape and distribution of moving parts, especially of the blades, and of stationary parts, struts in particular. Like with tire treads, and similar to the principle of acoustic diffusors, an irregular shape and distribution can flatten the noise spectrum, making the noise sound less disturbing. Tae Kim. "Reduction of Tonal Propeller Noise by Means of Uneven Blade Spacing". p. 4 M. Boltezar; M. Mesaric; A. Kuhelj. "The influence of uneven blade spacing on the SPL and noise spectra radiated from radial fans".
The inlet shape of the fan can also influence the noise levels generated by the fan.
Health organizations offer varying guidance on fan usage in high temperatures. The Centers for Disease Control and Prevention (CDC) advises against fan use when temperatures exceed 32.2 °C (90 °F), while the World Health Organization (WHO) suggests avoiding fan use above 40 °C (104 °F).
Recent studies have shed further light on this issue, though their findings are somewhat contradictory. One study found limited additional benefit from fan use above 35 °C (95 °F), while another study reported a 31% reduction in cardiac stress among elderly individuals using fans at 38 °C (100 °F).
The fan is often connected to machines with a rotating part rather than being powered separately. This is commonly seen in motor vehicles with internal combustion engines, 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 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, other methods may drive fans. High-pressure gases such as steam can drive a small turbine, and high-pressure liquids can drive a pelton wheel, either of 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 required for efficient fan operation.
A typical example uses a detached 10-watt, solar panel and is supplied with appropriate brackets, Power cable, and 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 .
The detached solar panel is typically installed in the spot that 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.
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