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..
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.
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).
Examples of axial fans are:
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.
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.
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.