Information about Computer Fan

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.

Akasa, Arctic Cooling, Delta, Nexus, Noctua, NorthQ, ebmpapst, Zalman are brands of fans.

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. The temperatures of 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 convection (passive cooling), more efficient cooling has become a necessity on many components. 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 surface area available for heat conduction, 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 retail Intel Pentium (released in 1993), 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 RAM and hard drives 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.

Power Supply fan

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. PSUs 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 140 watts^[3]), so efficient cooling is especially important. Passive coolers for new video cards, however, are not unheard of, notably the Thermalright HR-03 among others.

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.

Physical characteristics

The width and height of these usually square fans are measured in millimeters, with common sizes including 60 mm, 80 mm, 92 mm and 120 mm. Round fans 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 120mm fan with 90mm holes). The amount of airflow which these fans generate is 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), by the computer hardware or by software.

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 can fail at higher temperatures, and may perform poorly when mounted in any orientation other than horizontally. The lifespan of a sleeve bearing fan may be around 40,000 hours at 50°C. Fans that use sleeve bearings are generally cheaper and quieter than fans that use ball bearings.^[4]
• Ball bearing' fans use a sealed bearing containing steel balls against which the axle rotates. Though generally more expensive and noisier, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, and can be more durable, especially at higher temperatures. The lifespan of a ball bearing fan may be around 63,000 hours at 50°C.^[4]
• Fluid bearing fans have the advantages of silent operation and high life expectancy (comparable to ball bearing fans). However, these fans tend to be the most expensive.
• Magnetic bearing or Maglev fans, in which the fan is repelled from the motor by magnetism.

Connector pin assignment

Typical Fan

	P1	Black	Ground
	P2	Red	+12 Volt, +5 Volt, or 230 Volt in reverse order of importance
	P3	Yellow	Speed sensor wire (RPM)

PWM Fan^[5]

	P1	Black	Ground
	P2	Yellow	+12 Volt
	P3	Green	Speed sensor wire (RPM)
	P4	Blue	PWM (Pulse-width modulation) control wire

The behaviour of a PWM fan plugged into a 3-pin header (i.e. PWM signal disconnected) varies depending on model. Intel CPU coolers run at their fastest speed, as a failsafe (but can be slowed by connecting pins 4-1); others may run at the lowest speed (but can be operated at the fastest speed by joining pins 4-2) [2]

Alternatives

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

• Underclocking/undervolting to reduce power dissipation (this is the inverse of the "diminishing returns" problem faced by overclockers)
• Larger heatsink (for example, some motherboards have northbridge fans; others have larger, more costly heatsinks)
• Convection cooling: carefully designed, correctly oriented, and sufficiently large CPU coolers can dissipate up to 100W by convection alone.
• More unusual solutions, e.g. heatpipes bonded to the metal case, water cooling.

See also

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

References

External links

• 4-Wire Pulse Width Modulation (PWM) Controlled Fans Revision 1.3