Ceiling fan
A ceiling fan is a mechanical fan mounted on the ceiling of a room or space, usually electrically powered, suspended from the ceiling of a room, that uses hub-mounted rotating blades to circulate air. Ceiling fans typically rotate more slowly than other types of circulating fans, such as electric desk fans. They cool people effectively by introducing slow movement into the otherwise still, hot air of a room. Fans never actually cool air, unlike air-conditioning equipment, they in fact heat the air due to the waste heat from the motor and friction, but use significantly less power (cooling air is thermodynamically expensive). Conversely, a ceiling fan can also be used to reduce the stratification of warm air in a room by forcing it down to affect both occupants' sensations and thermostat readings, thereby improving climate control energy efficiency.
Computer fan
Fans may be mounted next to or onto a hard disk drive for cooling purposes. Hard drives can produce considerable heat over time, and are heat sensitive components that should not operate at excessive temperatures. In many situations, natural convective cooling suffices, but in some cases fans may be required. These may include -Fans are, less commonly, used for other purposes such as:Due to the low pressure, high volume air flows they create, most fans used in computers are of the axial flow type; centrifugal and crossflow fans type. Two important functional specifications are the airflow that can be moved, typically stated in cubic feet per minute (CFM), and static pressure. Given in decibels, the sound volume figure can be also very important for home and office computers; larger fans are generally quieter for the same CFM.