Design

The design of Phase Change systems should be centered mostly on preventing condensation from ruining a perfectly good computer. Those who decide to use Phase Change would do well to take precautions by heavily insulating their setups, and even using plastic sealant, to ensure protection from moisture.

Phase changing systems are available ready-built from companies like Vapochill and Prometia. OCZ, a company known for memory and power supplies, also recently dipped their toes in the phase change cooling market when they introduced their “Cryo-Z” Phase Change unit at CES in January of this year. The unit is expected to cost around $300 and be just as effective as more expensive systems. Regardless of the cost, all phase change units work in the same way.

The phase change process is a cycle that involves the transformation of a gas into a liquid, and then back again, hence “phase change.” As hinted before, the substance that is being manipulated in a phase change system is called the refrigerant. There are certain properties of some gases that make them desirable refrigerants. A good refrigerant is both safe to use and non-corrosive. These aspects will allow it to be have more widespread applications, with a low amount of maintenance. Other beneficial characteristics come from the thermodynamic properties of the compound: high latent heat of vaporization, low boiling point, and high density in gaseous form.

Condenser
Starting off arbitrarily along the phase change cycle, we have the condenser. At the condenser, heat is removed from the refrigerant. The refrigerant enters the condenser as a high pressure gas, and through forced convection it is cooled down enough to change back into a liquid. Expectedly, the condenser is nothing more than your standard heatsink design with tubes of refrigerant running throughout.

Capillary Tube
The capillary tube is simply a restrictive tube in the cycle that maintains different pressures on opposing sides. After passing the capillary tube, the refrigerant will be at a much lower pressure than it was after leaving the condenser. Physics dictate that as pressure decreases, so does temperature. This means that the refrigerant leaving the capillary tube is extremely cold.

Evaporator
The evaporator is the part of a phase change system that does the actual cooling. The shape of this unit depends on its application. If you have a Phase Change system chilling the coolant in a water cooling setup, then it will be probably wrapped around the water cooling tube to absorb heat from the water in some way or another. If you have the Phase Change system applied directly to your components, then it will be a block that sits directly atop the component. Heat is transferred from whichever is hot, your component or the water, to the refrigerant inside of the evaporator.

Compressor
The compressor is what really forces the whole phase change cycle to take place. The compressor is a pump that compresses the refrigerant vapor (thereby increasing its temperature and pressure) and pushes it through the rest of the cycle again.

Latent Heat
The thermodynamic property that drives the entire Phase Change cycle is something called latent heat. Latent heat is the reason that you cannot heat water to a temperature above 100°C, its boiling point. When you are actively heating water and it reaches 100°C, any extra heat you add to it is called the latent heat of vaporization. Eventually, it will turn into steam after absorbing a further 2260 kJ of heat. The amount of heat added differs between separate compounds. The principle of latent heat is used extensively in the Phase Change system, primarily in the chemical design of the refrigerant itself.

Bottom Line

You have a Phase Change system in the refrigerator in your kitchen. The technology has been used for quite a long time - in different applications, of course. In computers, Phase Change systems are used to produce subzero temperatures throughout the entire system. For people trying to overclock their systems to speeds that are significantly above and beyond anything normally achievable, Phase Change is the only way to go. However, cost, risk, and arcane difficulty installing parts are factors that make most overclockers pursue other, less complicated paths.