A computer fan can be 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 and/or other hardware to cool a computer is sometimes referred to as active cooling.
Manufacturers of fans include, among others, Akasa, Arctic Cooling, Cooler Master, Delta, Nexus, Noctua, NorthQ, ebm-papst, Scythe, 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 reasonable 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 (or free) convection (passive cooling), more effective cooling has become a necessity on many components. To cool these components, fans are used to move dead 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 PSU (power supply unit) has always used 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 GPU (graphics processing unit) on many modern graphics cards requires a heatsink and fan. In some cases, the northbridge chip on the motherboard requires a fan and heatsink. Other components such as the hard drives and RAM (More commonly RAM is cooled with attached RAM Heatsinks) 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. The most common RAM cooling application are RAM Heatsinks, which attach to the RAM itself. [1]
Cooling fan applications
Case mount
Used to aerate the case of the computer. The components inside the case which use active cooling cannot remove 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 generator of heat. Case fans are usually 80 mm, 92 mm or 120 mm along each side. Because 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 or made of UV-reactive plastic. Decorative grilles are also common. 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. Many modern PSUs expel the air from the rear, but only from the PSU itself. PSs with two fans are also available, which have a large fan on the bottom for removing case air and a smaller one on the back for expelling the warm air at a faster rate.
CPU fan
Used to cool the CPU (central processing unit).
See computer spot cooling.
Graphics card fan
Used to cool the GPU and/or memory on graphics cards. These fans were not necessary on older cards because of their low heat 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 (over 190 watts[2]), so efficient 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 or 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 where heat production is higher.
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 if the computer does not need much 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 an expense of airflow, but with much 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.[3][4]
Rifle bearing fans are similar to sleeve bearing, but are even 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.[5] The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
Ball bearing fans use a sealed bearing containing steel balls against which the axle rotates. 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.[3][4]
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[6].
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
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 outter-most edge of one long side. The size and spacing of the pin sockets is identical to a standard 3-pin female IC connector.
4-pin Molex connector
this connector is used when connecting the fan directly to the power supply. It consists of to 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.
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