Learning Resources
 

Cooling


Computer cooling is required to remove the waste heat produced by computer components, to keep components within permissible operating temperature limits.

Components that are susceptible to temporary malfunction or permanent failure if overheated include integrated circuits such as CPUs, chipset, graphics cards, and hard disk drives.

Components are often designed to generate as little heat as possible, and computers and operating systems may be designed to reduce power consumption and consequent heating according to workload, but more heat may still be produced than can be removed without attention to cooling. Use of heatsinks cooled by airflow reduces the temperature rise produced by a given amount of heat. Attention to patterns of airflow can prevent the development of hotspots. Computer fans are very widely used to reduce temperature by actively exhausting hot air. There are also more exotic and extreme techniques, such as liquid cooling.

Many computers are designed to sound an alarm or switch off if certain critical internal temperatures exceed a specified limit.

Cooling may be designed to reduce the ambient temperature within the case of a computer e.g. by exhausting hot air, or to cool a single component or small area (spot cooling). Components commonly individually cooled include the CPU, GPU and the northbridge chip.

Cooling can be hindered by:

Dust acting as a thermal insulator and impeding airflow, thereby reducing heat sink and fan performance.
Poor airflow including turbulence due to friction against impeding components such as ribbon cables, or improper orientation of fans, can reduce the amount of air flowing through a case and even create localized whirlpools of hot air in the case. In some cases of equipment with bad thermal design, cooling air can easily flow out through "cooling" holes before passing over hot components; cooling in such cases can often be improved by blocking of selected holes.
Poor heat transfer due to poor thermal contact between components to be cooled and cooling devices. This can be improved by the use of thermal compounds to even out surface imperfections, or even by lapping.


Desktop computers typically use one or more fans for cooling. Almost all desktop power supplies have at least one fan to exhaust air from the case. Most manufacturers recommend bringing cool, fresh air in at the bottom front of the case, and exhausting warm air from the top rear.

If fans are fitted to force air into the case more effectively than it is removed, the pressure inside becomes higher than outside, referred to as a "positive" airflow (the opposite case is called "negative" airflow). There are some claims that positive airflow results less dust in the case. To solve the dust problem, some models are fitted with dust filters but these must be periodically cleaned up.

The air flow inside the typical desktop case is usually not strong enough for a passive CPU heatsink. Most of desktop heat sinks are active, including one or even multiple directly attached fans.

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Heat-sinks
A component may be fitted in good thermal contact with a heatsink, a passive device with large thermal capacity and with a large surface area relative to its volume. Heatsinks are usually made of a metal with high thermal conductivity such as aluminium or copper, and incorporate fins to increase surface area. Heat from a relatively small component is transferred to the larger heatsink; the equilibrium temperature of the component plus heatsink is much lower than the component's alone would be. Heat is carried away from the heatsink by airflow, either due to natural convection or by forced-air fan airflow. Fan cooling is often used to cool processors and graphics cards of high electrical power. In a computer a typical heat-generating component may be manufactured with a flat surface; a block of metal with a corresponding flat surface and finned construction, sometimes with a fan attached, is clamped to the component. To fill poorly conducting air gaps due to imperfectly flat and smooth surfaces, a thin skim of thermal grease, a thermal pad, or thermal adhesive may be interposed between the component and heatsink.

An image of heat-sink