Editing Computer cooling (section)

===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.)