Computer fan - AbsoluteAstronomy.com

A computer fan is any fan

Fan (mechanical)

A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air.A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually, it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing...

inside, or attached to, a computer case

Computer case

A computer case is the enclosure that contains most of the components of a computer...

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

Ram

-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...

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

Convection

Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

(passive cooling

Passive cooling

Passive cooling refers to technologies or design features used to cool buildings without power consumption, such as those technologies discussed in the Passive house project.-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

IBM PC compatible

IBM PC compatible computers are those generally similar to the original IBM PC, XT, and AT. Such computers used to be referred to as PC clones, or IBM clones since they almost exactly duplicated all the significant features of the PC architecture, facilitated by various manufacturers' ability to...

market, the computer's power supply unit

Power supply

A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...

(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

Intel 80486

The Intel 80486 microprocessor was a higher performance follow up on the Intel 80386. Introduced in 1989, it was the first tightly pipelined x86 design as well as the first x86 chip to use more than a million transistors, due to a large on-chip cache and an integrated floating point unit...

, 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

Pentium 4

Pentium 4 was a line of single-core desktop and laptop central processing units , introduced by Intel on November 20, 2000 and shipped through August 8, 2008. They had a 7th-generation x86 microarchitecture, called NetBurst, which was the company's first all-new design since the introduction of the...

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

Graphics processing unit

A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...

(GPU) on many modern graphics cards also requires a heatsink and fan. In some cases, the northbridge

Northbridge (computing)

The northbridge has historically been one of the two chips in the core logic chipset on a PC motherboard, the other being the southbridge. Increasingly these functions have migrated to the CPU chip itself, beginning with memory and graphics controllers. For Intel Sandy Bridge and AMD Fusion...

chip on the motherboard

Motherboard

In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...

has another fan and heatsink. Other components such as the hard drives and RAM may also be actively cooled, though this remains relatively unusual. It is not uncommon to find five or more fans in a modern PC.

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 LED

LEd

LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

s, made of UV-reactive plastic, and covered with decorative grilles. Decorative fans and accessories are popular with case modders

Case modding

Case modification is the modification of a computer chassis , or a video game console chassis. Modifying a computer case in any non-standard way is considered a case mod...

. Air filter

Air filter

A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...

s are often used over intake fans, to prevent dust

Dust

Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...

from entering the case.

A power supply

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

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), so effective cooling is especially important. Passive coolers for new video cards, however, are not unheard of, such as the Thermalright

Thermalright

Thermalright is a Taiwan-based company that manufactures high-quality, high-performance aftermarket heat sinks for desktop computers. Thermalright products are primarily marketed towards gamer and enthusiasts who commonly overclock different parts of their computer, generating large amounts of...

HR-03.

Chipset fan

Used to cool the heatsink of the northbridge of a motherboard's chipset

Chipset

A chipset, PC chipset, or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.- Computers :...

; this may be needed where the system bus

System bus

A system bus is a single computer bus that connects the major components of a computer system. The technique was developed to reduce costs and improve modularity....

is significantly overclocked

Overclocking

Overclocking is the process of operating a computer component at a higher clock rate than it was designed for or was specified by the manufacturer, but some manufacturers purposely underclock their components to improve battery life. Many people just overclock or 'rightclock' their hardware to...

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
Peripheral Component Interconnect
Conventional PCI is a computer bus for attaching hardware devices in a computer...

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

Case modding

Case modification is the modification of a computer chassis , or a video game console chassis. Modifying a computer case in any non-standard way is considered a case mod...

, 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

Revolutions per minute

Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...

(RPM). Where noise is an issue large, slower-turning fans are quieter, and sensors and circuits can be used that reduce fan speed

Fan control

Fan control is the management of the rotational speed of an electric fan. There are many types of electric fans and many types of fan controls. This article principally describes the control of a computer fan, to provide adequate cooling while lowering noise....

, 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

Bearing (mechanical)

A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...

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. 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.
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. The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
Ball bearings
Ball bearing
A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit...

: 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.
Fluid bearing
Fluid bearing
Fluid bearings are bearings which support the bearing's loads solely on a thin layer of liquid or gas.They can be broadly classified as fluid dynamic bearings or hydrostatic bearings. Hydrostatic bearings are externally pressurized fluid bearings, where the fluid is usually oil, water or air, and...

s have the advantages of near-silent operation and high life expectancy (comparable to ball bearings), but tend to be the most expensive.
Magnetic bearing
Magnetic bearing
A magnetic bearing is a bearing which supports a load using magnetic levitation. Magnetic bearings support moving machinery without physical contact; for example, they can levitate a rotating shaft and permit relative motion with very low friction and no mechanical wear...

s or maglev
Magnetic levitation
Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields...

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. 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

Molex connector

Molex connector is the vernacular term for a two-piece pin and socket interconnection, most frequently disk drive connectors. Pioneered by Molex Connector Company, the two-piece design became an early electronic standard. Molex developed and patented the first examples of this connector style in...

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

Tachometer

A tachometer is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute on a calibrated analogue dial, but digital displays are increasingly common...

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

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

Pulse-width modulation

Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....

signal to provide variable speed control. 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

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.

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
  Convection
  Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
  
  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
  Underclocking
  Underclocking, also known as downclocking, is the practice of modifying a synchronous circuit's timing settings to run at a lower clock rate than it was specified to operate at. It may be said to be the computer equivalent of driving a car below the speed limit...
  
  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.

Other methods of cooling include:

- Water cooling
- Refrigeration
  Refrigeration
  Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
- Ionic wind
  Ion wind
  Ion wind, ionic wind, or coronal wind is a stream of ionized fluid generated by a strong electric field. Francis Hauksbee, curator of instruments for the Royal Society of London, made the earliest report of electric wind in 1709...
  
  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. http://www.technologyreview.com/computing/22668/?a=f and http://www.technologyreview.com/computing/19285/?a=f

Usage of a cooling fan

Case mount

CPU fan

Graphics card fan

Chipset fan

Other types of fans

Appearance

Physical characteristics

Fan sizing

Fan connector

Alternatives

See also