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Please note: Do It Yourself articles and guides are intended for technically advanced users. Please review important cautionary information at the end of this page. Republished articles presented in the Do It Yourself section do not necessarily reflect the opinions or positions of AMD.
Heat Pipes
“Mime”
The development of faster microprocessors goes hand-in-hand with the development of ways to dissipate the heat they generate.
Conventional heatsinks are designed to have the largest possible surface area and a fan to pull away heat. But as clock speeds and heat loads increase, they run into design limitations, both size and noise wise – the larger the fan, the greater the racket. Short of switching to a new cooling method, the solution to these issues is to modify the conventional heatsink.
General Rules of Heat Transfer
Generally, heat seeks to achieve balance by traveling from something hot to something cold. There are three basic methods of heat transfer – conduction, convection, and radiation:
- Conduction is the direct exchange of heat energy between two materials
- Convection is the transfer of heat to a surrounding gas or liquid, such as air or water – “forced” convection is the forcing away by fan or pump of that gas or liquid
- Radiation, or radiant cooling, is the escape of electromagnetic radiation – it does not rely on another substance, and can occur even in a vacuum
As far as computer systems are concerned, conduction and convection are, for now at least, far more significant than radiation.
Conduction: Metals and their Limits
A common way to change the thermal conductivity of a heatsink is to change the material used to manufacture it.
Aluminum is commonly used because of its decent thermal conductivity and the fact it is easily and relatively cheaply machined. Copper is a much better conductor, but is heavier and more difficult to work with, and thus more expensive. Silver is a better conductor still, but is far more expensive. There are limits to the values of all these metals, and therefore limits to using conduction to cool microprocessors, because thermal conductivity declines as temperatures rise and impurities in metals reduce heat transfer efficiency. Some manufacturers now mix copper and aluminum in hybrid heatsinks that do not fully match the heat transfer of pure copper, but are cheaper and lighter.
Convection: Heat Pipes
Heat pipes, which are small, sealed, and curved copper tubes, offer perhaps the most effective way to increase the thermal performance of a conventional heatsink at a reasonable price.
They are self-contained, phase-change cooling devices that take advantage of changes in heat to convert a liquid – called the “working liquid” – into vapor and then back again. When a liquid changes phase to a vapor, the vapor absorbs heat, is transported away from the heat source, and then releases heat when it condenses back into liquid. The heat released is dissipated and the cycle repeats.
The easiest way to explain heat pipes is to break them into three sections, the evaporator section, the adiabatic section, and the condenser section:
- In the evaporator section, the working fluid is heated to its boiling point and converted into a vapor that travels along the adiabatic section and on to the condenser section
- Because the vapor holds almost all the heat while moving from one end of the pipe to another, the adiabatic section is named for a process in which little heat is gained or lost
- In the condenser section the vapor is condensed back into liquid form, the heatsink dissipates the released latent heat, and the capillary wicking surface returns the working fluid back to the evaporator section
The AMD Athlon™ 64 FX processor employs a futuristic four-heat-pipe design that increases the effectiveness of the heatsink without creating more noise and without significantly adding to its overall size or weight. In particular, this design allows enthusiasts to play extreme games without overtaxing the system.
Cautionary Statement
Activities and projects described herein may involve the use of tools and materials that may present health and safety hazards. These must be handled carefully and all tools and products should be used strictly according to manufacturers’ precautions and instructions for the safe use of the respective tool or product. The techniques described herein may result in the voiding of manufacturers’ warranties. The user assumes all risks associated with the techniques described in this article/guide. THIS INFORMATION IS PROVIDED “AS IS” WITH NO WARRANTY, EXPRESS OR IMPLIED. AMD ASSUMES NO RESPONSIBILITY FOR ANY ERRORS CONTAINED IN THIS ARTICLE/GUIDE AND HAS NO LIABILITY OR OBLIGATION FOR ANY DAMAGES ARISING FROM OR IN CONNECTION WITH THE USE OF THIS ARTICLE/GUIDE.
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