Computer Cooling - Phase-change 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 which usually sits underneath the PC, with a tube leading to the processor. Inside the unit is a compressor of the same type as in a window air conditioner. The compressor compresses a gas (or mixture of gases) which compresses it into a liquid. Then, the liquid is pumped up to the processor, where it passes through a condenser (heat dissipation device) and then an expansion device to vaporize the fluid, 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 −15 to −150 degrees Celsius. The gas flows down to the compressor and the cycle begins over again. This way, the processor can be cooled to temperatures ranging from −15 to −150 degrees Celsius, 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 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 cooling system is being developed, inserting a pump into the thermo siphon 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 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 media, 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.