Computer fan

A 3D illustration of four 80 mm fans, a type of fan commonly used in personal computers (sometimes as a set, or mixed with other fan sizes).

A computer fan is any fan inside, or attached to, 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.

Usage of a cooling fan

As processors, graphics cards, RAM and other components in computers have increased in 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.^[1] 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.^[1] 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^[update] this remains relatively unusual. It is not uncommon to find five or more fans in a modern PC.

Cooling fan application

An 80x80x25mm 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 in width and length. 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. Effective cooling of a concentrated heat source such as a large-scale integrated circuit requires a heatsink, which may be cooled by a fan; use of a fan alone will not prevent overheating of the small chip.

See computer spot cooling.

Graphics card fan

Used to cool the heatsink of 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 (dissipating up to 289 watts^[2]), 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 heatsink of the northbridge of a motherboard's chipset; this may be needed where the system bus is significantly overclocked and dissipates more power than is usual, but may otherwise be unnecessary.

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.

Appearance

Many gamers, case modders, and enthusiasts utilize fans illuminated with colored LED lights.

Physical characteristics

Square-framed fans are usually used, but round frames are also used, often so that a larger fan than the mounting holes would otherwise allow can be used (e.g., a 120 mm fan with holes for the corners of a 90 mm square fan). The width of square fans and the diameter of round ones are usually stated in millimeters; common sizes include 40, 60, 80, 92, and 120 mm. Heights are typically 10 or 20 mm, but this is usually not an important dimension as it does not affect mounting holes or apertures in the case. The airflow that fans generate is typically stated in cubic feet per minute (CFM), and the speed of rotation in revolutions per minute (RPM). Where noise is an issue large, slower-turning fans are quieter, and sensors and circuits can be used that reduce fan speed, and hence noise, when temperature is not high.

The other consideration when choosing a computer fan is static pressure. A fan with high static pressure is more effective at forcing air through restricted spaces, such as the gaps between a radiator or heatsink; static pressure is more important than CFM when choosing a fan for use with a heatsink. The relative importance of static pressure depends on the degree to which the airflow is restricted by geometry; static pressure becomes more important as the spacing between heatsink fins decreases. Static pressure is usually stated in either mm Hg or mm H₂O.

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 bearings use two surfaces lubricated with oil or grease as a friction contact. They often use porous sintered sleeves to be self-lubricating, requiring only infrequent maintenance or replacement. Sleeve bearings are less durable at higher temperatures as the contact surfaces wear and the lubricant dries up, eventually leading to failure; however, lifetime is similar at relatively low ambient temperatures^[3]. 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 become noisy as they age.^[3]
• Rifle bearings are similar to sleeve bearings, 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.^[4] The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
• Ball bearings: Though generally more expensive, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, are more durable at higher temperatures, and are quieter than sleeve-bearing fans at higher rotation speeds. The lifespan of a ball bearing fan may be over 60,000 hours at 50 °C.^[3]
• Fluid bearings have the advantages of near-silent operation and high life expectancy (comparable to ball bearings), but tend to be the most expensive.
• Magnetic bearings or maglev bearings, in which the fan is repelled from the bearing by magnetism.

Fan sizing

Fans are available in many sizes and capacities. Typically 120mm case and power supply fans are used where cooling requirements are demanding, as for computers used to play games, and for quieter operation at lower speeds; cheaper 80mm fans are used for less demanding cases. In general, the faster the fan, the noisier it is. Within a given physical size capacity is roughly proportional to current draw^{[citation needed]}. For a given flow a larger fan will be quieter than a smaller fan.

Fan connector

Connectors usually used for computer fans (there is no agreed standard) 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 of receptacle is 22-01-3037. Molex Part number of individual crimp contacts is 08-55-0101. Matching PCB header Molex 22-23-2031

4-pin Molex connector KK Family

This is a special variant of the Molex KK connector with four pins but with the locking/polarisation features of a 3-pin connector. The additional pin is used for a pulse-width modulation signal to provide variable speed control.^[5] These can be plugged into 3-pin headers, but will lose their fan speed control. Molex Part number of receptacle is 47054-1000. Molex Part number of individual crimp contacts is 08-55-0101. Molex Part number of the header is 47053-1000.

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. This is the same connector as used on hard drives before the SATA became standard.

Dell 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. Some improvement can be achieved by eliminating all fans except one in the power supply which also draws hot air out of the case.^[6]

• Systems can be designed to use passive cooling alone, reducing noise and eliminating moving parts that may fail This can be achieved by:
  • Natural convection cooling: carefully designed, correctly oriented, and sufficiently large heatsinks can dissipate up to 100 W by natural convection alone
  • Heatpipes to transfer heat out of the case
  • Undervolting or underclocking to reduce power dissipation
  • Sinking motherboards in liquid oil provides excellent convection cooling and protects from humidity and water without the need for heatsinks or fans. Special care must be taken to ensure compatibility with adhesives and sealants used on the motherboard and ICs. This solution is used in some external environments such as wireless equipment located in the wild.^{[citation needed]}

Other methods of cooling include:

• • Water cooling
  • Refrigeration
  • Ionic wind cooling is being researched, whereby air is moved by ionizing air between 2 electrodes. This replaces the fan and has the advantage of no moving parts. [1] and [2]

See also

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

References

1. ^ ^{a b} Mueller, Scott 2005. Upgrading and Repairing PCs. Que Publishing. 16th edition. pp 1274-1280
2. ^ "Nvidia Reveals GeForce GTX 295 Specs". http://www.maximumpc.com/article/news/nvidia_reveals_geforce_gtx_295_specs. Retrieved 2009-08-17. 
3. ^ ^{a b c} Williams, Melody. "Ball vs Sleeve: A Comparison in Bearing Performance". http://www.nmbtc.com/pdf/engineering/fans_ball_vs_sleeve.pdf. Retrieved 2007-10-30. 
4. ^ "Coolermaster Neon LED Case Fans Review". 2003-03-25. http://www.overclockersclub.com/reviews/coolermasterledcasefans/. Retrieved 2007-12-05. 
5. ^ "4-Wire PWM Controlled Fans Specification". 2005-09. http://www.formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf. Retrieved 2009-12-11. 
6. ^ Silent PC Review Recommended Power Supplies, http://www.silentpcreview.com/Recommended_PSUs, retrieved 2010-08-01 .