Phase-change cooling, also called vapor cooling, is a microprocessor-cooling technology that works according to the same principles as a conventional refrigerator, freezer or air conditioner.
The principal components of a phase-change cooling system are the compressor (or condenser), the vaporizer, the radiating element and the pump. In the compressor, a refrigerant gas condenses into a volatile liquid. The pump moves the liquid to the vaporizer, where the pressure is reduced and the liquid returns to the gaseous phase, absorbing thermal energy. When strategically placed in a computer system, the vaporizer can effectively remove thermal energy from the microprocessor and other critical components. The heated gas is then recycled through the radiating element and back to the compressor, where a new cycle begins. In this way, thermal energy is constantly removed from the computer components and transferred to the external environment.
With phase-change cooling, microprocessors can be chilled to temperatures at or below the freezing point of water. For this reason, humidity controls are necessary to prevent condensation of water vapor as dew or frost inside the computer housing. Phase-change cooling, while effective, is expensive. Most phase-change cooling systems also tend to be noisy although this problem can be mitigated by the use of acoustic shielding.
In September 2008, Cray, the supercomputer company, announced a new type of phase-change cooling called ECOphlex (short for PHase-change Liquid EXchange) that is expected to enable multiple petaflop speeds and simultaneously save energy. Cray XT5 systems will ship with the new technology.
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