The best CPU cooling solutions: from minimal to extreme

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By Jeremy Cook

Computers require electrical energy to operate. At the CPU level, much of this input energy is turned into heat as it churns through 1s and 0s. Therefore, engineers have to consider thermal issues and CPU cooling when designing a computer in order to avoid “cooking” equipment under heavy load. It’s a simple concept: extract more heat than the amount of thermal energy generated by the processor, accounting for spikes in usage.

In this article, we will look at the CPU cooling types available, from very simple—or nonexistent—to extremes that are rarely applied in real-life scenarios.


No added CPU cooling: it’s OK (maybe)

In many cases with simple units, CPU cooling is not part of the design. Consider the energy efficient ATTiny series of microcontrollers. Their minuscule power requirements mean that the tiny amount of heat generated is easily dissipated. In other cases, such as Raspberry Pi single-board computers (SBCs), heat buildup can be more of a problem. However, if you’re not doing anything too intensive with the processor, it’s typically able to shed sufficient heat without issue. CPU heat buildup and dissipation are cumulative, so while a short spike in activity might not trigger any thermal alarms, a sustained thermal load can be a problem.

In the Raspberry Pi’s case, the CPU’s operation is throttled when it is too hot, so you (hopefully) won’t permanently damage your hardware. At the same time, this means you’re forgoing performance that would be easily accessible with added cooling.


Basic CPU cooling: heat sink plus fan

The most basic cooling method is to apply a heat sink directly to the processor using thermal paste or thermal tape (collectively referred to as TIM, or thermal interface material). A heat sink, often made from highly thermally conductive copper or aluminum, essentially multiplies the surface area through which heat can escape your processor.

In a heat exchanger role, copper offers better thermal conductivity (~400W/m*k) than aluminum (~200W/m*k). Copper is, however, more expensive than aluminum and heavier. While you may not directly select the material when purchasing a heat exchanger, it’s still something to be aware of.

To further enhance thermal dissipation, using a CPU cooling fan to actively blow air over a heat sink can greatly improve performance as cooler air is constantly circulated over the fins . The downside here is that fans themselves require energy, a controller (unless they run constantly), and produce noise. Fans can also wear out over time and this constant circulation of air can introduce dust inside the system.


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Enhanced CPU cooling: heat pipes and vacuum chambers (plus fan)

The next step up from a solid metal heat sink is to use heat pipes and/or a vacuum chamber. Both devices use a thermal fluid (often simply water) that evaporates when heated by a processor, thus absorbing heat. In the case of heat pipes, the evaporated fluid transports thermal energy through the pipes to a cooler area. It then condenses (releasing thermal energy) and returns to the hotter CPU area via a wicking surface under capillary action.

A vacuum chamber works using the same evaporation/condensation cycle of heat pipes. Instead of taking the form of a long (often bent) tube, vacuum chambers typically take the form of a flat square that sits directly on top of a processor. Inside the thin evacuated chamber, fluid evaporates and condenses, spreading heat from one area to another. A heat sink, fan, and/or heat pipes can be used in conjunction with a vacuum chamber for an enhanced cooling setup.

These methods meet most computer cooling needs, but perhaps you need something even better. There are three more extreme CPU cooling methods in practice today.


Extreme CPU cooling #1: liquid heat transport and heat pumps

CPU water cooling works in a similar manner to an internal combustion vehicle’s cooling system: circulating a cooling fluid (water) from a hot processing unit to an external radiative cooling unit. As with most methodologies, this sort of water CPU cooling can be combined with other methods (e.g., fans, fins) to make the most of it.

Water cooling is seen in high-end gaming rigs and custom PCs. If you want to get more extreme with fluid heat transport, you could implement a phase-change unit (i.e., a heat pump) that is mechanically similar to a refrigerator. This will easily mitigate the heat of nearly any processor, but it’s so unusual for CPU cooling that it’s more of an expensive prototype and/or demo proposition as of this writing.


Extreme CPU cooling #2: liquid immersion cooling

Another option is to submerge your electronics in a cooling fluid, typically mineral oil. The mineral oil can absorb heat energy to keep components cool, though how well it dissipates heat over longer CPU loads depends on several factors. There are no fans to maintain, but mineral oil does eventually evaporate and/or get dirty. A vat of liquid ready to explode onto the floor or wick out through cables can also be problematic.

While direct liquid cooling might be impractical for home PCs or servers, it’s actually a very old idea by computing standards. The CRAY-2 supercomputer—the fastest computer in the world when released in 1985—successfully used direct liquid cooling, allowing the massively powerful (for its day) processing unit to fit into a relatively compact 53-inch (135cm) diameter. Processor-heated liquid was transported to an external “waterfall” cooling unit, reportedly earning it the nickname, “bubbles.”


Extreme CPU cooling #3: low-temperature location


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One more extreme solution: why not just move your processor from a hot geographic environment to a cooler one? At a consumer level, this rarely makes sense—perhaps apart from keeping your personal server in a cold basement—but for a large enterprise, it’s worth consideration. Meta (then Facebook) opened a near-Arctic server farm in 2013 in Luleå, Sweden, 70 miles from the Arctic Circle. It reportedly uses nearly 40% less power than a traditional data center. While the benefits appear significant, ten years later there doesn’t appear to be a cold-weather computing land rush, perhaps owing to infrastructure and connectivity challenges. For more on data center-level server cooling, be sure to check out this article.

Processor cooling: always needed (but often it happens naturally)

At the end of the day, many processors will run without issue sans heat sink. People have reportedly come up with creative solutions like attaching a penny to a computing device for a bit of extra thermal mass in a pinch. At the same time, there are many instances where you can’t get the needed performance without also worrying about extracting heat. Overclocked processors come to mind.

Whatever your application, don’t forget about the heat implications. There are a wide variety of ways to keep things cool when needed, and it can be useful to step back to the drawing board and consider the different options.



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