Computer fan

A set of 4 industry standard 80 mm fans, most commonly used in personal computers.

A computer fan is any fan inside a computer case used for cooling purposes, and may refer to fans that draw cooler air into the case from the outside, expel warm air from inside, or move air across a heatsink to cool a particular component. The use of fans to cool a computer is an example of active cooling.

Manufacturers of fan include, among others, AVC, Akasa, Antec, Arctic Cooling, Cooler Master, Delta, ebm-papst, Nexus, Nidec, Noctua, NorthQ, Scythe, Sharkoon, Thermaltake, Y.S. Tech and Zalman.

Usage

As processors, graphics cards, RAM and other components in computers have increased in clock speed and power consumption, the amount of heat produced by these components as a side-effect of normal operation has also increased. These components need to be kept within a specified temperature range to prevent overheating, instability, malfunction and damage leading to a shortened component lifespan.

While in earlier personal computers it was possible to cool most components using natural convection (passive cooling), many modern components require more effective active cooling. To cool these components, fans are used to move heated air away from the components and draw cooler air over them. Fans attached to components are usually used in combination with a heatsink to increase the area of heated surface in contact with the air, thereby improving the efficiency of cooling.

In the IBM compatible PC market, the computer's power supply unit (PSU) almost always uses an exhaust fan to expel warm air from the PSU. Active cooling on CPUs started to appear on the Intel 80486, and by 1997 was standard on all desktop processors. Chassis or case fans, usually one exhaust fan to expel heated air from the rear and optionally an intake fan to draw cooler air in through the front, became common with the arrival of the Pentium 4 in late 2000. A third vent fan in the side of the PC, often located over the CPU, is also common. The graphics processing unit (GPU) on many modern graphics cards also requires a heatsink and fan. In some cases, the northbridge chip on the motherboard has another fan and heatsink. Other components such as the hard drives and RAM may also be actively cooled, though as of 2007 this remains relatively unusual. It is not uncommon to find five or more fans in a modern PC.

Cooling fan applications

A computer fan

Case mount

Used to aerate the case of the computer. The components inside the case cannot dissipate heat efficiently if the surrounding air is too hot. Case fans move air through the case, usually drawing cooler outside air in through the front (where it may also be drawn over the internal hard drive racks) and expelling it through the rear. There may be a third fan in the side or top of the case to draw outside air into the vicinity of the CPU, which is usually the largest single heat source. Standard case fans are 80 mm, 92 mm or 120 mm along each side. As case fans are often the most readily visible form of cooling on a PC, decorative fans are widely available and may be lit with LEDs, made of UV-reactive plastic, and covered with decorative grilles. Decorative fans and accessories are popular with case modders. Air filters are often used over intake fans, to prevent dust from entering the case.

A power supply (PSU) fan often plays a double role, not only keeping the PSU itself from overheating, but also removing warm air from inside the case. PSUs with two fans are also available, which typically have a fan on the inside to supply case air into the PSU and a second fan on the back to expel the heated air.

CPU fan

Used to cool the CPU (central processing unit) heatsink.

See computer spot cooling.

Graphics card fan

Used to cool the graphics processing unit or the memory on graphics cards. These fans were not necessary on older cards because of their low power dissipation, but most modern graphics cards, especially those designed for 3D graphics and gaming, need their own dedicated cooling fans. Some of the higher powered cards can produce more heat than the CPU (up to 289 watts), so effective cooling is especially important. Passive coolers for new video cards, however, are not unheard of, such as the Thermalright HR-03.

Chipset fan

Used to cool the northbridge of a motherboard's chipset, which may be necessary for system bus overclocking.

Other types of fans

Other less commonly encountered fans may include:

• PCI slot fan: A fan mounted in one of the PCI slots, usually to supply additional cooling to the PCI and/or graphics cards.
• Hard disk fan: A fan mounted next to or on a hard disk drive. This may be desirable on faster-spinning (e.g. 10,000 RPM) hard disks with greater heat production.
• CD burner fan: Some internal CD and/or DVD burners included cooling fans.

Physical characteristics

The width and height of these usually square fans are measured in millimeters; common sizes include 60 mm, 80 mm, 92 mm and 120 mm. Fans with a round frame are also available; these are usually designed so that one may use a larger fan than the mounting holes would otherwise allow (i.e., a 120 mm fan with 90 mm holes). The amount of airflow which fans generate is typically measured in cubic feet per minute (CFM), and the speed of rotation is measured in revolutions per minute (RPM). Often, computer enthusiasts choose fans which have a higher CFM rating, but produce less noise (measured in decibels, or dB), and some fans come with an adjustable RPM rating to produce less noise when the computer does not require additional airflow. Fan speeds may be controlled manually (a simple potentiometer control, for example), thermally, or by the computer hardware or by software. It is also possible to run many 12V fans from the 5 V supply, at the expense of airflow, but with reduced noise levels.

The type of bearing used in a fan can affect its performance and noise output. Most computer fans use one of the following bearing types:

• Sleeve bearing fans use two surfaces lubricated with oil or grease as a friction contact. Sleeve bearings are less durable as the contact surfaces can become rough and/or the lubricant dry up, eventually leading to failure. Sleeve bearings may be more likely to fail at higher temperatures, and may perform poorly when mounted in any orientation other than vertical. The lifespan of a sleeve bearing fan may be around 40,000 hours at 50 °C. Fans that use sleeve bearings are generally cheaper than fans that use ball bearings, and are quieter at lower speeds early in their life, but can grow considerably noisier as they age.
• Rifle bearing fans are similar to sleeve bearing, but are quieter and have almost as much lifespan as ball bearings. The bearing has a spiral groove in it that pumps fluid from a reservoir. This allows them to be safely mounted horizontally (unlike sleeve bearings), since the fluid being pumped lubricates the top of the shaft. The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
• Ball bearing fans use ball bearings. Though generally more expensive, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, are more durable especially at higher temperatures, and quieter than sleeve bearing fans at higher rotation speeds. The lifespan of a ball bearing fan may be around 63,000 hours at 50 °C.
• Fluid bearing fans have the advantages of near-silent operation and high life expectancy (comparable to ball bearing fans). However, these fans tend to be the most expensive. The enter bearing fan is a variation of the fluid bearing fan, developed by Everflow.
• Magnetic bearing or maglev fans, in which the fan is repelled from the bearing by magnetism.

Fan connector

The standard connectors for computer fans are

3-pin Molex connector KK Family

This connector is used when connecting a fan to the motherboard or other circuit board. It is a small thick rectangular in-line female connector with two tabs on the outer-most edge of one long side. The size and spacing of the pin sockets is identical to a standard 3-pin female IC connector. The three pins are used for ground, +12 V power, and a tachometer signal. Molex Part number 22013037.

4-pin Molex connector KK Family

This connector is compatible with the 3-pin version, with the additional pin used for a pulse-width modulation signal to provide variable speed control.

4-pin Molex connector

This connector is used when connecting the fan directly to the power supply. It consists of two wires (red/12V and black/ground) leading to and splicing into a large in-line 4-pin male-to-female Molex connector.

Dell, Inc. proprietary

This connector is an expansion of a simple 3-pin female IC connector by adding two tabs to the middle of the connector on one side and a lock-tab on the other side. The size and spacing of the pin sockets is identical to a standard 3-pin female IC connector and 3-pin Molex connector. Some models have the wiring of the white wire (speed sensor) in the middle, whereas the standard 3-pin Molex requires the white wire as pin #3, thus compatibility issues may exist.

Alternatives

If a fan is not desirable, because of noise, reliability, or environmental concerns, there are some alternatives:

• Many computers, such as simple home computers and business computers, can rely on passive cooling alone and do not require a case fan to keep computer components at ordinary operating temperatures.
• Undervolting and/or underclocking to reduce power dissipation
• Larger heatsinks (for example, some motherboards have northbridge fans; others have larger, more costly heatsinks)
• Natural convection cooling: carefully designed, correctly oriented, and sufficiently large CPU coolers can dissipate up to 100 W by natural convection alone
• More unusual solutions, e.g. heatpipes bonded to the metal case, water cooling, or refrigeration
• Motherboards sunk in liquid oil provides excellent convection cooling and protects from humidity and water without the need for heatsinks or fans. This solution is used in some external environments like wireless equipments located in the wild.

See also

• Fan (mechanical)
• Centrifugal fan
• Computer cooling
• PC fan control
• Quiet PC
• SpeedFan