Editing Computer cooling (section)

==Other techniques==
===Liquid immersion cooling===
<!--Full immersion cooling links here-->
{{main|Server immersion cooling}}
[[File:Toby and the Mineral Oil Cooled Rig (4958369451).jpg|thumb|A computer immersed in mineral oil]]
Another growing trend due to the increasing heat density of computers, GPUs, FPGAs, and [[application-specific integrated circuit|ASIC]]s is to immerse the entire computer or select components in a [[thermal conduction|thermally, but not electrically, conductive]] liquid. Although rarely used for the cooling of personal computers,<ref>{{cite web|url=http://www.eppenga.com/photos/fluid-cooled-pc/liquid-pc-technical.html|title=Liquid PC Technical – Eppenga Website|first=Ebo|last=Eppenga|website=eppenga.com|access-date=25 July 2014|archive-url=https://web.archive.org/web/20140812063836/http://www.eppenga.com/photos/fluid-cooled-pc/liquid-pc-technical.html|archive-date=12 August 2014|url-status=live}}</ref> liquid immersion is a routine method of cooling large power distribution components such as [[Distribution transformer|transformers]]. It is also becoming popular with data centers.<ref>{{cite web|url=http://www.datacenterknowledge.com/archives/2013/07/01/the-immersion-data-center/|title=The Immersion Data Center: The New Frontier of High-Density Computing|date=1 July 2013|access-date=25 July 2014|archive-url=https://web.archive.org/web/20140727084549/http://www.datacenterknowledge.com/archives/2013/07/01/the-immersion-data-center/|archive-date=27 July 2014|url-status=live}}</ref><ref name="facebook-immersion">{{cite web|url=http://www.datacenterknowledge.com/archives/2012/12/21/facebook-tests-immersion-cooling/|title=Facebook Tests Immersion Cooling|date=21 December 2012|access-date=25 July 2014|archive-url=https://web.archive.org/web/20140727102138/http://www.datacenterknowledge.com/archives/2012/12/21/facebook-tests-immersion-cooling/|archive-date=27 July 2014|url-status=live}}</ref> Personal computers cooled in this manner may not require either fans or pumps, and may be cooled exclusively by [[Thermosiphon|passive heat exchange]] between the computer hardware and the enclosure it is placed in.<ref name="facebook-immersion"/><ref>{{cite web|url=http://www.eppenga.com/photos/fluid-cooled-pc/liquid-cooled-pc.html|title=Liquid Cooled PC – Eppenga Website|first=Ebo|last=Eppenga|website=eppenga.com|access-date=25 July 2014|archive-url=https://web.archive.org/web/20140812065345/http://www.eppenga.com/photos/fluid-cooled-pc/liquid-cooled-pc.html|archive-date=12 August 2014|url-status=live}}</ref> A heat exchanger (i.e. [[heater core]] or radiator) might still be needed though, and the piping also needs to be placed correctly.<ref>{{Cite web|url=http://www.iceotope.com/the-science|archive-url=https://web.archive.org/web/20140728123429/http://www.iceotope.com/the-science|url-status=dead|title=Iceotope hardware case, note that 2 hot pipes are present in the plastic box holding the hardware (functioning as coolant reservoir), of which one -the hot pipe- is placed at the top, and the other -the cold one- at the bottom|archive-date=28 July 2014}}</ref>

The coolant used must have sufficiently low [[electrical conductivity]] not to interfere with the normal operation of the computer. If the liquid is somewhat electrically conductive, it may cause electrical shorts between components or traces and permanently damage them.<ref>Tom's Hardware – "[http://www.tomshardware.com/2006/01/09/strip_out_the_fans/ Strip Out The Fans]", 9 January 2006, presented as 11 web pages.</ref> For these reasons, it is preferred that the liquid be an insulator ([[dielectric]]) and not conduct electricity.

A wide variety of liquids exist for this purpose, including [[transformer oil]]s, synthetic single-phase and dual phase dielectric coolants such as [[3M]] [[Fluorinert]] or 3M Novec. Non-purpose oils, including cooking, motor and [[silicone oil]]s, have been successfully used for cooling personal computers.

Some fluids used in immersion cooling, especially hydrocarbon based materials such as mineral oils, cooking oils, and organic esters, may degrade some common materials used in computers such as rubbers, [[polyvinyl chloride]] (PVC), and [[thermal grease]]s. Therefore it is critical to review the material compatibility of such fluids prior to use. Mineral oil in particular has been found to have negative effects on PVC and rubber-based wire insulation.<ref>{{cite web|url=https://www.pugetsystems.com/submerged.php|title=Mineral Oil Cooled PC – Project Ready DIY Kit for the PC Enthusiast|website=pugetsystems.com|access-date=19 December 2018|archive-url=https://web.archive.org/web/20181215174126/https://www.pugetsystems.com/submerged.php|archive-date=15 December 2018|url-status=live}}</ref> Thermal pastes used to transfer heat to heatsinks from processors and graphic cards has been reported to dissolve in some liquids, however with negligible impact to cooling, unless the components were removed and operated in air.<ref>{{Cite web|url=https://www.youtube.com/watch?v=sSnGmAqQaFs|title=Parts from the Oil-cooled PC – Do they still work???|date=22 February 2018 |via=www.youtube.com|access-date=19 December 2018|archive-url=https://web.archive.org/web/20180226005901/https://www.youtube.com/watch?v=sSnGmAqQaFs|archive-date=26 February 2018|url-status=live}}</ref>

Evaporation, especially for 2-phase coolants, can pose a problem,<ref>{{Cite web|url=https://www.engineeredfluids.com/immersioncooling|title=Engineered Fluids {{!}} Single-Phase Immersion Cooling|website=Dielectric Coolants {{!}} United States {{!}} Engineered Fluids|language=en|access-date=2019-01-21|archive-url=https://web.archive.org/web/20190122043912/https://www.engineeredfluids.com/immersioncooling|archive-date=22 January 2019|url-status=live}}</ref> and the liquid may require either to be regularly refilled or sealed inside the computer's enclosure. Immersion cooling can allow for extremely low [[Power usage effectiveness|PUE]] values of 1.05, vs air cooling's 1.35, and allow for up to 100&nbsp;KW of computing power (heat dissipation, TDP) per [[19-inch rack]], as opposed to air cooling, which usually handles up to 23&nbsp;KW.<ref>{{Cite web|url=https://www.datacenterknowledge.com/power-and-cooling/five-reasons-data-center-liquid-cooling-rise|title=Five Reasons Data Center Liquid Cooling Is on the Rise|date=23 July 2018|website=Data Center Knowledge}}</ref>

===Waste heat reduction===
Where powerful computers with many features are not required, less powerful computers or ones with fewer features can be used. {{As of|2011}} a [[VIA Technologies|VIA]] [[EPIA]] motherboard with CPU typically dissipates approximately 25&nbsp;watts of heat, whereas a more capable Pentium 4 motherboard and CPU typically dissipates around 140&nbsp;watts. Computers can be powered with [[direct current]] from an external [[power supply]] unit which does not generate heat inside the computer case. The replacement of [[cathode-ray-tube]] (CRT) displays by more efficient thin-screen [[liquid crystal display]] (LCD) ones in the early twenty-first century has reduced power consumption significantly.

===Heat-sinks===
{{Main|Heat sink}}
{{multiple image
 | total_width = 370
 | image1      = Harumphy.dg965.heatsink.jpg
 | caption1    = Passive heatsink on a chipset
 | image2      = Heatsink with heat pipes.jpg
 | caption2    = Active heatsink with a fan and [[heat pipe]]s
 }}
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,<ref>The thermal conductivity and thermal capacity of silver is better than that of copper, which is better than that of aluminium (see [[List of thermal conductivities]]). Consequently on purely technical grounds, solid silver (silver-plating is pointless) is better than copper, which is better than aluminium, for heatsinks and also for saucepans. Cost, of course, rules out silver, although enthusiasts have used silver heatsinks [http://www.pcstats.com/articleview.cfm?articleID=1116 and silver saucepans are used for cooking when cost is not an issue] {{Webarchive|url=https://web.archive.org/web/20150716233230/http://www.pcstats.com/articleview.cfm?articleID=1116 |date=16 July 2015 }}</ref> 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 convective or fan-forced airflow. Fan cooling is often used to cool processors and graphics cards that consume significant amounts of electrical energy. 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 an attached fan, is clamped to the component. To fill poorly conducting air gaps due to imperfectly flat and smooth surfaces, a thin layer of [[thermal grease]], a [[Thermally conductive pad|thermal pad]], or [[thermal adhesive]] may be placed between the component and heatsink.

Heat is removed from the heatsink by [[convection]], to some extent by [[Radiative cooling|radiation]], and possibly by [[Thermal conduction|conduction]] if the heatsink is in thermal contact with, say, the metal case. Inexpensive fan-cooled [[aluminium]] heatsinks are often used on standard desktop computers. Heatsinks with [[copper]] base-plates, or made of copper, have better thermal characteristics than those made of aluminium. A copper heatsink is more effective than an aluminium unit of the same size, which is relevant with regard to the high-power-consumption components used in high-performance computers.

Passive heatsinks are commonly found on older CPUs, parts that do not dissipate much power (such as the chipset), computers with low-power processors, and equipment where silent operation is critical and fan noise unacceptable.

Usually a heatsink is clamped to the integrated heat spreader (IHS), a flat metal plate the size of the CPU package which is part of the CPU assembly and spreads the heat locally. A thin layer of thermal compound is placed between them to compensate for surface imperfections. The spreader's primary purpose is to redistribute heat. The heatsink fins improve its efficiency.

[[File:Memoria DDR3 Patriot Viper PVS34G1333LLK - 2.JPG|thumb|Memory modules fitted with a finned heatsink]]
Several brands of DDR2, DDR3, DDR4 and DDR5 DRAM memory modules are fitted with a finned heatsink clipped onto the top edge of the module. The same technique is used for video cards that use a finned passive heatsink on the GPU.

Higher-end M.2 SSDs can be prone to significant heat generation, and as a result these may be sold with a heatsink included, or alternatively a third-party heatsink may be attached by the user during installation.

Fan-cooled aluminium heatsinks were originally the norm for desktop computers, but nowadays many heatsinks feature copper base-plate, copper base-circle, or are entirely made of copper.

Dust tends to build up in the crevices of finned heatsinks, particularly with the high airflow produced by fans. This keeps the air away from the hot component, reducing cooling effectiveness; however, removing the dust restores effectiveness.

===Peltier (thermoelectric) cooling===
{{Main|Thermoelectric cooling}}
[[File:Regular Peltier cooling setup for PC.png|thumb|Regular Peltier cooling setup for PCs]]

Peltier junctions are generally only around 10–15% as efficient as the ideal [[refrigerator]] ([[Carnot cycle]]), compared with 40–60% achieved by conventional compression cycle systems (reverse [[Rankine cycle|Rankine]] systems using compression/expansion).<ref>{{Cite web|url=http://www.pnl.gov/main/publications/external/technical_reports/pnnl-19259.pdf|title=The Prospects of Alternatives to Vapor Compression Technology for Space Cooling and Food Refrigeration Applications|access-date=23 January 2013|archive-url=https://web.archive.org/web/20130306021637/http://www.pnl.gov/main/publications/external/technical_reports/PNNL-19259.pdf|archive-date=6 March 2013|url-status=live}}</ref> Due to this lower efficiency, thermoelectric cooling is generally only used in environments where the solid state nature (no [[moving parts]], low maintenance, compact size, and orientation insensitivity) outweighs pure efficiency.

Modern TECs use several stacked units each composed of dozens or hundreds of thermocouples laid out next to each other, which allows for a substantial amount of [[heat transfer]]. A combination of [[bismuth]] and [[tellurium]] is most commonly used for the thermocouples.

As active heat pumps which consume power, TECs can produce temperatures below ambient, impossible with passive heatsinks, radiator-cooled [[#Liquid cooling|liquid cooling]], and heatpipe HSFs. However, while pumping heat, a Peltier module will typically consume more electric power than the heat amount being pumped.

It is also possible to use a Peltier element together with a high pressure refrigerant (two phase cooling) to cool the CPU.<ref>Kijk magazine, 2, 2020</ref><ref>{{Cite web|url=https://www.incooling.com/technology/|title=Technology &#124; Incooling|website=www.incooling.com|access-date=5 March 2020|archive-date=17 April 2021|archive-url=https://web.archive.org/web/20210417123011/https://www.incooling.com/technology/|url-status=dead}}</ref>

===Liquid cooling===
{{further|topic=water cooling|Water cooling#Computer usage}}

[[File:Deepcool cooler.png|thumb|right|An all-in-one (AIO) cooling unit, installed in a case]]
[[File:PC watercooling T-Line-2009-12-03.jpg|thumb|left|[[Do it yourself|DIY]] water cooling setup showing a 12&nbsp;V pump, CPU [[waterblock]] and the typical application of a [[T-Line]]]]
[[File:Liquid cooling schematic.png|thumb|left|Schematic of a regular liquid cooling setup for PCs]]

Liquid cooling is a highly effective method of removing excess heat, with the most common [[Coolant|heat transfer fluid]] in desktop PCs being (distilled) water. The advantages of water cooling over [[air cooling]] include water's higher [[specific heat capacity]] and [[thermal conductivity]].

The principle used in a typical (active) liquid cooling system for computers is identical to that used in an automobile's [[internal combustion engine]], with the water being circulated by a water pump through a water block mounted on the CPU (and sometimes additional components as GPU and northbridge)<ref name="auto">{{cite web|url=http://computer.howstuffworks.com/liquid-cooled-pc2.htm|title=How Liquid-cooled PCs Work|date=24 August 2006|access-date=24 July 2014|archive-url=https://web.archive.org/web/20140721124907/http://computer.howstuffworks.com/liquid-cooled-pc2.htm|archive-date=21 July 2014|url-status=live}}</ref> and out to a [[heat exchanger]], typically a [[radiator]]. The radiator is itself usually cooled additionally by means of a [[Computer fan|fan]].<ref name="auto"/> Besides a fan, it could possibly also be cooled by other means, such as a Peltier cooler (although Peltier elements are most commonly placed directly on top of the hardware to be cooled, and the coolant is used to conduct the heat away from the hot side of the Peltier element).<ref>{{cite web|url=http://computer.howstuffworks.com/liquid-cooled-pc5.htm|title=How Liquid-cooled PCs Work|date=24 August 2006|access-date=25 July 2014|archive-url=https://web.archive.org/web/20140729200304/http://computer.howstuffworks.com/liquid-cooled-pc5.htm|archive-date=29 July 2014|url-status=live}}</ref><ref>{{cite web|url=http://www.tomshardware.co.uk/forum/282844-29-peltier-water-cooling|title=TEC/Peltier CPU Chilled Water Cooling – Overclocking|website=Tom's Hardware|access-date=24 July 2014|archive-url=https://web.archive.org/web/20140808074239/http://www.tomshardware.co.uk/forum/282844-29-peltier-water-cooling|archive-date=8 August 2014|url-status=live}}</ref> A coolant reservoir is often also connected to the system.<ref>{{cite web|url=http://www.techradar.com/news/computing-components/upgrades/pc-water-cooling-guide-all-you-need-to-know-952521|title=PC water cooling guide: all you need to know|date=8 May 2011|access-date=24 July 2014|archive-url=https://web.archive.org/web/20140728040240/http://www.techradar.com/news/computing-components/upgrades/pc-water-cooling-guide-all-you-need-to-know-952521|archive-date=28 July 2014|url-status=live}}</ref>

Besides active liquid cooling systems, passive liquid cooling systems are also sometimes used.<ref>{{cite web|url=http://www.techradar.com/news/computing-components/upgrades/pc-water-cooling-guide-all-you-need-to-know-952521/2#articleContent|title=PC water cooling guide: all you need to know|date=8 May 2011|access-date=25 July 2014|archive-url=https://web.archive.org/web/20140728102802/http://www.techradar.com/news/computing-components/upgrades/pc-water-cooling-guide-all-you-need-to-know-952521/2#articleContent|archive-date=28 July 2014|url-status=live}}</ref><ref>{{cite web|url=http://www.tomshardware.com/news/silverstone-td04-pumpless-liquid-cooling,27023.html|title=SilverStone Reveals Pumpless Liquid Cooling System|date=10 June 2014}}</ref><ref>{{cite web|url=http://www.overclockers.com/cpu-vapor-cooling-thermosyphon/|title=CPU Vapor Cooling Thermosyphon – Overclockers|date=4 November 2005|access-date=25 July 2014|archive-url=https://web.archive.org/web/20140727122319/http://www.overclockers.com/cpu-vapor-cooling-thermosyphon/|archive-date=27 July 2014|url-status=live}}</ref><ref>{{cite web|url=http://www.overclock.net/t/607208/water-cooling-without-pump/30|title=Water Cooling Without Pump – Page 4 – Overclock.net – An Overclocking Community|website=overclock.net|date=26 May 2011 |access-date=25 July 2014|archive-url=https://web.archive.org/web/20140812174650/http://www.overclock.net/t/607208/water-cooling-without-pump/30|archive-date=12 August 2014|url-status=live}}</ref><ref>{{cite web|url=http://www.xtremesystems.org/forums/showthread.php?218039-passive-pumpless-watercooling|title=passive pumpless watercooling|website=xtremesystems.org|access-date=25 July 2014|archive-url=https://web.archive.org/web/20140811130340/http://www.xtremesystems.org/forums/showthread.php?218039-passive-pumpless-watercooling|archive-date=11 August 2014|url-status=live}}</ref> These systems often leave out a fan or a water pump, theoretically increasing their reliability and making them quieter than active systems. The downsides of these systems are that they are much less efficient in discarding the heat and thus need   much more coolant{{Mdash}}and a commensurately larger reservoir{{Mdash}} to give it time to cool down.

Liquids allow the transfer of more heat from the parts being cooled than air, making liquid cooling suitable for overclocking and high performance computer applications.<ref name="hardwidge">{{cite book|last=Hardwidge|first=Ben|title=Building Extreme PCs: The Complete Guide to Modding and Custom PCs|publisher=O'Reilly Media|isbn=978-0-596-10136-7|pages=66–70|url=https://books.google.com/books?id=ISZnhgYdzIcC&pg=PA72|year=2006}}</ref> Compared to air cooling, liquid cooling is also influenced less by the ambient temperature.<ref>{{cite web|url= http://www.avadirect.com/forum/Blog/11472-Ambient-Temperatures-Effect-on-PC-Cooling/|title= Ambient Temperatures Effect on PC Cooling|author= <!--Staff writer(s); no by-line.-->|date= 17 January 2014|website= Avadirect|access-date= 27 January 2017|archive-url= https://web.archive.org/web/20170202062704/http://www.avadirect.com/forum/Blog/11472-Ambient-Temperatures-Effect-on-PC-Cooling/|archive-date= 2 February 2017|url-status= live}}</ref> Liquid cooling's comparatively low noise level compares favorably to that of air cooling, which can become quite noisy.

Disadvantages of liquid cooling include complexity and the potential for a coolant leak. Leaking water (and any additives in the water) can damage electronic components with which it comes into contact, and the need to test for and repair leaks makes for more complex and less reliable installations.<ref>{{Cite web |title=Look what's inside Linus Torvalds' latest Linux development PC |url=https://www.zdnet.com/article/look-whats-inside-linus-torvalds-latest-linux-development-pc/ |access-date=2024-11-22 |website=ZDNET |language=en}}</ref> (The first major foray into the field of liquid-cooled personal computers for general use, the high-end versions of [[Apple Inc.|Apple]]'s [[Power Mac G5]], was ultimately doomed by a propensity for coolant leaks.<ref name="PowerMac G5 Coolant Leaks/Repairs">{{cite web |url=http://www.xlr8yourmac.com/systems/G5_coolant_leaks.html |title=PowerMac G5 Coolant Leaks/Repairs. |access-date=15 July 2013 |publisher=XLR8yourmac |archive-url=https://web.archive.org/web/20170626164703/http://www.xlr8yourmac.com/systems/G5_coolant_leaks.html |archive-date=26 June 2017 |url-status=live }}</ref>) An air-cooled heatsink is generally much simpler to build, install, and maintain than a water cooling solution,<ref name="murphy">{{cite journal|last=Murphy|first=Dave|title=Maintain Your Water-Cooling Setup|journal=Maximum PC Magazine|date=September 2007|pages=58–60|url=https://books.google.com/books?id=OQIAAAAAMBAJ&pg=PA58}}</ref> although CPU-specific water cooling kits can also be found, which may be just as easy to install as an air cooler. These are not limited to CPUs, and liquid cooling of GPU cards is also possible.<ref>{{cite web|url=http://www.legitreviews.com/nzxt-kraken-g10-gpu-water-cooler-review-on-an-amd-radeon-r9-290x_130344|title=NZXT Kraken G10 GPU Water Cooler Review on an AMD Radeon R9 290X – Legit Reviews|date=10 December 2013|access-date=11 December 2013|archive-url=https://web.archive.org/web/20131213080732/http://www.legitreviews.com/nzxt-kraken-g10-gpu-water-cooler-review-on-an-amd-radeon-r9-290x_130344|archive-date=13 December 2013|url-status=live}}</ref>

While originally limited to [[Mainframe computer|mainframe]] computers, liquid cooling has become a practice largely associated with [[overclocking]] in the form of either manufactured all-in-one (AIO) kits or do-it-yourself setups assembled from individually gathered parts.<ref>{{Cite web |date=2022-05-06 |title=Featured Projects – LiquidHaus |url=https://www.liquidhaus.com/pages/gallery |access-date=2022-05-06 |website= |archive-url=https://web.archive.org/web/20220506071434/https://www.liquidhaus.com/pages/gallery |archive-date=6 May 2022 |url-status=dead}}</ref> The past few years{{when|date=November 2021}} have seen an increase in the popularity of liquid cooling in pre-assembled, moderate to high performance, desktop computers. Sealed ("closed-loop") systems incorporating a small pre-filled radiator, fan, and waterblock simplify the installation and maintenance of water cooling at a slight cost in cooling effectiveness relative to larger and more complex setups. Liquid cooling is typically combined with air cooling, using liquid cooling for the hottest components, such as CPUs or GPUs, while retaining the simpler and cheaper air cooling for less demanding components.

The IBM [[Aquasar]] system uses ''hot water cooling'' to achieve [[Efficient energy use|energy efficiency]], the water being used to heat buildings as well.<ref>{{Cite web|url=http://www.hpcwire.com/hpcwire/2010-07-02/ibm_hot_water-cooled_supercomputer_goes_live_at_eth_zurich.html|archive-url=https://web.archive.org/web/20120813212211/http://www.hpcwire.com/hpcwire/2010-07-02/ibm_hot_water-cooled_supercomputer_goes_live_at_eth_zurich.html|url-status=dead|title=HPC Wire July 2, 2010 |archive-date=13 August 2012}}</ref><ref>{{cite web|url=http://news.cnet.com/8301-11128_3-20004543-54.html|title=IBM liquid-cooled supercomputer heats building|date=10 May 2010|access-date=28 September 2011|archive-url=https://web.archive.org/web/20131101060256/http://news.cnet.com/8301-11128_3-20004543-54.html|archive-date=1 November 2013|url-status=live}}</ref>

Since 2011, the effectiveness of water cooling has prompted a series of all-in-one (AIO) water cooling solutions.<ref>{{cite web|last1=Jeremy|title=Air Cooling Vs Liquid Cooling For Pc What To Choose|url=http://gamesngearselite.com/air-cooling-vs-liquid-cooling/|website=gamesngearselite|access-date=8 February 2017|archive-url=https://web.archive.org/web/20170211091531/http://gamesngearselite.com/air-cooling-vs-liquid-cooling/|archive-date=11 February 2017|url-status=live}}</ref> AIO solutions result in a much simpler to install the unit, and most units have been reviewed positively by review sites.

===Heat pipes and vapor chambers===
{{Main|Heat pipe}}

[[Image:Radeon 9600XT Heatpipe passive cooling.jpg|thumb|A graphics card with a fanless heatpipe cooler design]]

A heat pipe is a hollow tube containing a heat transfer liquid. The liquid absorbs heat and evaporates at one end of the pipe. The vapor travels to the other (cooler) end of the tube, where it condenses, giving up its [[latent heat]]. The liquid returns to the hot end of the tube by gravity or [[capillary action]] and repeats the cycle. Heat pipes have a much higher effective thermal conductivity than solid materials. For use in computers, the heatsink on the CPU is attached to a larger radiator heatsink. Both heatsinks are hollow, as is the attachment between them, creating one large heat pipe that transfers heat from the CPU to the radiator, which is then cooled using some conventional method. This method is usually used when space is tight, as in small form-factor PCs and laptops, or where no fan noise can be tolerated, as in audio production. Because of the efficiency of this method of cooling, many desktop CPUs and GPUs, as well as high end chipsets, use heat pipes or vapor chambers in addition to active fan-based cooling and passive heatsinks to remain within safe operating temperatures. A vapor chamber operates on the same principles as a heat pipe but takes on the form of a slab or sheet instead of a pipe. Heat pipes may be placed vertically on top and form part of vapor chambers. Vapor chambers may also be used on high-end [[smartphones]].

===Electrostatic air movement and corona discharge effect cooling===
The cooling technology under development by Kronos and Thorn Micro Technologies employs a device called an ionic wind pump (also known as an electrostatic fluid accelerator). The basic operating principle of an ionic wind pump is [[corona discharge]], an electrical discharge near a charged conductor caused by the ionization of the surrounding air.

The corona discharge cooler developed by Kronos works in the following manner: A high electric field is created at the tip of the cathode, which is placed on one side of the CPU. The high energy potential causes the oxygen and nitrogen molecules in the air to become ionized (positively charged) and create a corona (a halo of charged particles). Placing a grounded anode at the opposite end of the CPU causes the charged ions in the corona to accelerate towards the anode, colliding with neutral air molecules on the way. During these collisions, momentum is transferred from the ionized gas to the neutral air molecules, resulting in movement of gas towards the anode.

The advantages of the corona-based cooler are its lack of moving parts, thereby eliminating certain reliability issues and operating with a near-zero noise level and moderate energy consumption.<ref>{{Cite web |url=https://thefutureofthings.com/3057-ionic-wind/ |title=Ionic Wind – Chillin' the PC |date=2 January 2007 |access-date=11 April 2021 |archive-url=https://web.archive.org/web/20130613114337/http://thefutureofthings.com/articles/46/ionic-wind-chillin-the-pc.html |archive-date=13 June 2013}}</ref>

===Soft cooling===
Soft cooling is the practice of utilizing software to take advantage of [[Power management|CPU power saving technologies]] to minimize energy use. This is done using [[HLT (x86 instruction)|halt]] instructions to turn off or put in standby state CPU subparts that aren't being used or by [[underclocking]] the CPU. While resulting in lower total speeds, this can be very useful if overclocking a CPU to improve [[user experience]] rather than increase raw processing power, since it can prevent the need for noisier cooling. Contrary to what the term suggests, it is not a form of cooling but of reducing heat creation.

===Undervolting===
[[Undervolting]] is a practice of running the CPU or any other component with voltages below the device specifications. An undervolted component draws less power and thus produces less heat. The ability to do this varies by manufacturer, product line, and even different production runs of the same product (as well as that of other components in the system), but processors are often specified to use voltages higher than strictly necessary. This [[Engineering tolerance|tolerance]] ensures that the processor will have a higher chance of performing correctly under sub-optimal conditions, such as a lower-quality motherboard or low power supply voltages. Below a certain limit, the processor will not function correctly, although undervolting too far does not typically lead to permanent hardware damage (unlike overvolting).

Undervolting is used for [[Quiet PC|quiet systems]], as less cooling is needed because of the reduction of heat production, allowing noisy fans to be omitted. It is also used when battery charge life must be maximized.

===Chip-integrated===
Conventional cooling techniques all attach their "cooling" component to the outside of the computer chip package. This "attaching" technique will always exhibit some thermal resistance, reducing its effectiveness. The heat can be more efficiently and quickly removed by directly cooling the local hot spots of the chip, within the package. At these locations, power dissipation of over 300&nbsp;W/cm<sup>2</sup> (typical CPU is less than 100&nbsp;W/cm<sup>2</sup>) can occur, although future systems are expected to exceed 1000&nbsp;W/cm<sup>2</sup>.<ref>{{cite journal |first=I. |last=Mudawar |title=Assessment of High-Heat-Flux Thermal Management Schemes |journal=IEEE Transactions on Components and Packaging Technologies |volume=24 |issue=2 |pages=122–141 |year=2001 |doi=10.1109/6144.926375 |url=https://engineering.purdue.edu/BTPFL/BTPFL%20Publications/83.pdf }}{{Dead link|date=December 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> This form of local cooling is essential to developing high power density chips. This ideology has led to the investigation of integrating cooling elements into the computer chip. Currently there are two techniques: micro-channel heatsinks, and jet impingement cooling.

In micro-channel heatsinks, channels are fabricated into the silicon chip (CPU), and coolant is pumped through them. The channels are designed with very large surface area which results in large heat transfers. Heat dissipation of 3000&nbsp;W/cm<sup>2</sup> has been reported with this technique.<ref>{{cite journal |first1=M. B. |last1=Bowers |first2=I. |last2=Mudawar |title=High Flux Boiling inLow Flow Rate, Low Pressure Drop Mini-Channel and Micro-Channel Heat Sinks |journal=[[International Journal of Heat and Mass Transfer]] |volume=37 |issue=2 |pages=321–332 |year=1994 |doi=10.1016/0017-9310(94)90103-1 |bibcode=1994IJHMT..37..321B }}</ref> The heat dissipation can be further increased if two-phase flow cooling is applied. Unfortunately, the system requires large pressure drops, due to the small channels, and the [[heat flux]] is lower with dielectric coolants used in electronic cooling.

Another local chip cooling technique is jet impingement cooling. In this technique, a coolant is flowed through a small orifice to form a jet. The jet is directed toward the surface of the CPU chip, and can effectively remove large heat fluxes. Heat dissipation of over 1000&nbsp;W/cm<sup>2</sup> has been reported.<ref>{{cite journal |first1=M. K. |last1=Sung |first2=I. |last2=Mudawar |title=Single-phase and two-phase hybrid cooling schemes for high-heat-flux thermal management of defense electronics |journal=Journal of Electronic Packaging |year=2009 |volume=131 |issue=2 |pages=021013 |doi=10.1115/1.3111253 }}</ref> The system can be operated at lower pressure in comparison to the micro-channel method. The heat transfer can be further increased using two-phase flow cooling and by integrating return flow channels (hybrid between micro-channel heatsinks and jet impingement cooling).

===Phase-change cooling===
Phase-change cooling is an extremely effective way to cool the processor. A vapor compression phase-change cooler is a unit that usually sits underneath the PC, with a tube leading to the processor. Inside the unit is a compressor of the same type as in an [[air conditioner]]. The compressor compresses a gas (or mixture of gases) which comes from the evaporator (CPU cooler discussed below). Then, the very hot high-pressure vapor is pushed into the condenser (heat dissipation device) where it condenses from a hot gas into a liquid, typically subcooled at the exit of the condenser then the liquid is fed to an expansion device (restriction in the system) to cause a drop in pressure a vaporize the fluid (cause it to reach a pressure where it can boil at the desired temperature); the expansion device used can be a simple capillary tube to a more elaborate thermal expansion valve. The liquid evaporates (changing phase), absorbing the heat from the processor as it draws extra energy from its environment to accommodate this change (see [[latent heat]]). The evaporation can produce temperatures reaching around {{convert|−15|to|−150|°C|abbr=on}}<!--guessing at identity of unidentified "degrees", assuming same as below-->. The liquid flows into the evaporator cooling the CPU, turning into a vapor at low pressure. At the end of the evaporator this gas flows down to the compressor and the cycle begins over again. This way, the processor can be cooled to temperatures ranging from {{convert|-15|to|-150|°C|abbr=on}}, depending on the load, wattage of the processor, the refrigeration system (see [[refrigeration]]) and the gas mixture used. This type of system suffers from a number of issues (cost, weight, size, vibration, maintenance, cost of electricity, noise, need for a specialized computer tower) but, mainly, one must be concerned with dew point and the proper insulation of all sub-ambient surfaces that must be done (the pipes will sweat, dripping water on sensitive electronics).

Alternately, a new breed of the cooling system is being developed, inserting a pump into the [[thermosiphon]] loop. This adds another degree of flexibility for the design engineer, as the heat can now be effectively transported away from the heat source and either reclaimed or dissipated to ambient. Junction temperature can be tuned by adjusting the system pressure; higher pressure equals higher fluid saturation temperatures. This allows for smaller condensers, smaller fans, and/or the effective dissipation of heat in a high ambient temperature environment. These systems are, in essence, the next generation fluid cooling paradigm, as they are approximately 10 times more efficient than single-phase water. Since the system uses a dielectric as the heat transport medium, leaks do not cause a catastrophic failure of the electric system.

This type of cooling is seen as a more extreme way to cool components since the units are relatively expensive compared to the average desktop. They also generate a significant amount of noise, since they are essentially refrigerators; however, the compressor choice and air cooling system is the main determinant of this, allowing for flexibility for noise reduction based on the parts chosen.

A "thermosiphon" traditionally refers to a closed system consisting of several pipes and/or chambers, with a larger chamber containing a small reservoir of liquid (often having a boiling point just above ambient temperature, but not necessarily). The larger chamber is as close to the heat source and designed to conduct as much heat from it into the liquid as possible, for example, a CPU cold plate with the chamber inside it filled with the liquid. One or more pipes extend upward into some sort of radiator or similar heat dissipation area, and this is all set up such that the CPU heats the reservoir and liquid it contains, which begins boiling, and the vapor travels up the tube(s) into the radiator/heat dissipation area, and then after condensing, drips back down into the reservoir, or runs down the sides of the tube. This requires no moving parts, and is somewhat similar to a heat pump, except that capillary action is not used, making it potentially better in some sense (perhaps most importantly, better in that it is much easier to build, and much more customizable for specific use cases and the flow of coolant/vapor can be arranged in a much wider variety of positions and distances, and have far greater thermal mass and maximum capacity compared to heat pipes which are limited by the amount of coolant present and the speed and flow rate of coolant that capillary action can achieve with the wicking used, often sintered copper powder on the walls of the tube, which have a limited flow rate and capacity.)

===Liquid nitrogen===
[[Image:2007TaipeiITMonth IntelOCLiveTest Overclocking-6.jpg|thumb|Liquid nitrogen may be used to cool overclocked components.]]

As [[liquid nitrogen]] boils at {{convert|-196|°C|abbr=on}}, far below the freezing point of water, it is valuable as an extreme coolant for short overclocking sessions.

In a typical installation of liquid nitrogen cooling, a copper or aluminium pipe is mounted on top of the processor or graphics card. After the system has been heavily insulated against condensation, the liquid nitrogen is poured into the pipe, resulting in temperatures well below {{convert|-100|°C|abbr=on}}.

Evaporation devices ranging from cut out heatsinks with pipes attached to custom milled copper containers are used to hold the nitrogen as well as to prevent large temperature changes. However, after the nitrogen evaporates, it has to be refilled. In the realm of personal computers, this method of cooling is seldom used in contexts other than [[overclocking]] trial-runs and record-setting attempts, as the CPU will usually expire within a relatively short period of time due to temperature [[Stress (physics)|stress]] caused by changes in internal temperature.

Although liquid nitrogen is non-flammable, it can condense [[oxygen]] directly from air. Mixtures of [[liquid oxygen]] and flammable materials can be [[oxyliquit|dangerously explosive]].

Liquid nitrogen cooling is, generally, only used for processor benchmarking, due to the fact that continuous usage may cause permanent damage to one or more parts of the computer and, if handled in a careless way, can even harm the user, causing [[frostbite]].

===Liquid helium===
[[Liquid helium]], colder than liquid nitrogen, has also been used for cooling. Liquid helium boils at {{convert|-269|°C|abbr=on}}, and temperatures ranging from {{convert|-230|to|-240|°C|abbr=on}} have been measured from the heatsink.<ref name="liquidhelium">{{cite web|url=https://www.youtube.com/watch?v=wB0JodKgZ0A|title=AMD Phenom II Overclocked to 6.5GHz – New World Record for 3DMark|last=AMDUnprocessed|date=14 February 2013|via=YouTube|access-date=1 December 2016|archive-url=https://web.archive.org/web/20160712065612/https://www.youtube.com/watch?v=wB0JodKgZ0A|archive-date=12 July 2016|url-status=live}}</ref> However, liquid helium is more expensive and more difficult to store and use than liquid nitrogen. Also, extremely low temperatures can cause integrated circuits to stop functioning. Silicon-based semiconductors, for example, will freeze out at around {{convert|-233|°C|abbr=on}}.<ref name="freezeout">{{cite web|url=http://www.extremetemperatureelectronics.com/tutorial3.html|title=Extreme-Temperature Electronics (Tutorial – Part 3)|website=extremetemperatureelectronics.com|access-date=11 March 2012|archive-url=https://web.archive.org/web/20120306214055/http://www.extremetemperatureelectronics.com/tutorial3.html|archive-date=6 March 2012|url-status=live}}</ref>