Editing Computer cooling (section)

===Airflow===

The colder the cooling medium (the air), the more effective the [[Heat Transfer|cooling]]. Cooling air temperature can be improved with these guidelines:
* Supply cool air to the hot components as directly as possible. Examples are air snorkels and tunnels that feed outside air directly and exclusively to the CPU or GPU cooler. For example, the [[BTX (form factor)|BTX]] case design prescribes a CPU air tunnel.
* Expel warm air as directly as possible. Examples are: Conventional PC ([[ATX]]) power supplies blow the warm air out the back of the case. Many dual-slot [[Video card|graphics card]] designs blow the warm air through the cover of the adjacent slot. There are also some [[Aftermarket (merchandise)|aftermarket]] coolers that do this. Some CPU cooling designs blow the warm air directly towards the back of the case, where it can be ejected by a case fan.
* Air that has already been used to spot-cool a component should not be reused to spot-cool a different component (this follows from the previous items). The BTX case design violates this rule, since it uses the CPU cooler's exhaust to cool the chipset and often the graphics card. One may come across old or ultra-low-budget ATX cases which feature a PSU mount in the top. Most modern ATX cases do however have a PSU mount in the bottom of the case with a filtered air vent directly beneath the PSU.
* Prefer cool intake air, avoid inhaling exhaust air (outside air above or near the exhausts). For example, a CPU cooling air duct at the back of a tower case would inhale warm air from a graphics card exhaust. Moving all exhausts to one side of the case, conventionally the back/top, helps to keep the intake air cool.
* Hiding cables behind motherboard tray or simply apply ziptie and tucking cables away to provide unhindered airflow.

Fewer fans strategically placed will improve the airflow internally within the PC and thus lower the overall internal case temperature in relation to ambient conditions. The use of larger fans also improves efficiency and lowers the amount of waste heat along with the amount of noise generated by the fans while in operation.

There is little agreement on the effectiveness of different fan placement configurations, and little in the way of systematic testing has been done. For a rectangular PC (ATX) case, a fan in the front with a fan in the rear and one in the top has been found to be a suitable configuration. However, AMD's (somewhat outdated) system cooling guidelines notes that "A front cooling fan does not seem to be essential. In fact, in some extreme situations, testing showed these fans to be recirculating hot air rather than introducing cool air."<ref>[http://support.amd.com/us/Processor_TechDocs/23794.pdf AMD Thermal, Mechanical, and Chassis Cooling Design Guide] {{Webarchive|url=https://web.archive.org/web/20110515181129/http://support.amd.com/us/Processor_TechDocs/23794.pdf |date=15 May 2011 }} – Although somewhat out of date, it appears to be backed up by some amount of systematic testing which is lacking in many other guides.</ref> It may be that fans in the side panels could have a similar detrimental effect – possibly through disrupting the normal air flow through the case. However, this is unconfirmed and probably varies with the configuration.

==== Air pressure ====
[[File:Computer cooling.svg|thumb|300px|1) Negative pressure &nbsp; &nbsp; 2) Positive pressure]]
Loosely speaking, positive pressure means intake into the case is stronger than exhaust from the case. This configuration results in pressure inside of the case being higher than in its environment. Negative pressure means exhaust is stronger than intake. This results in internal air pressure being lower than in the environment. Both configurations have benefits and drawbacks, with positive pressure being the more popular of the two configurations. Negative pressure results in the case pulling air through holes and vents separate from the fans, as the internal gases will attempt to reach an equilibrium pressure with the environment. Consequently, this results in dust entering the computer in all locations. Positive pressure in combination with filtered intake solves this issue, as air will only incline to be exhausted through these holes and vents in order to reach an equilibrium with its environment. Dust is then unable to enter the case except through the intake fans, which need to possess dust filters.