A computer fan is any fan inside, or attached to, a computer case used for active cooling. Fans are used to draw cooler air into the case from the outside, expel warm air from inside and move air across a heat sink to cool a particular component. Both axial and sometimes centrifugal (blower/squirrel-cage) fans are used in computers. Computer fans commonly come in standard sizes, such as 92 mm, 120 mm, 140 mm, and even 200–220 mm. Computer fans are powered and controlled using 3-pin or 4-pin fan connectors.
A 3D illustration of six 80 mm fans, a type of fan once commonly used in personal computers (sometimes as a set, or mixed with other fan sizes)
A 30-millimetre (1.2 in) PC fan laying atop one sized 250 mm (9.8 in)
An 80×80×25 mm axial computer fan
Fans from computer case – front and back
A fan is a powered machine used to create a flow of air. A fan consists of a rotating arrangement of 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 electric motors, but other sources of power may be used, including hydraulic motors, handcranks, and internal combustion engines.
A typical electric fan
A table fan
Fans are used to force air into low and high bypass jet engines, seen here on a Boeing 777.
Two c. 1980 box fans