Phase Change

You often hear about some group of nuts in Europe setting records for overclocking components far beyond their previously conceived maximums. Probably the most significant development in recent overclocking history occurred on October 17, 2005, when Sampsa Kurri from Muropaketti.com managed to run his brand new R520-based X1800XT above 1GHz. A GPU running above 1GHz produces absolutely insane amounts of raging, blistering heat. Simple water cooling couldn’t even deal with this kind of energy. Hence, Sampsa and his team of crazies utilized Liquid Nitrogen (LN2). LN2 can be obtained rather easily by the fractional distillation of air at 3000 PSI. This ease of production makes it pretty cheap – about 25 cents per liter if you don’t include the cost of highly insulated containers needed to store it in.

The boiling point of nitrogen (i.e. the temperature at which it turns into a gas) is -196C, very cold. With coldness we get something called condensation. If you’ve ever held a cold can of soda or a glass of iced tea outside on a warm summer day, you probably noticed the wetness that gathers on the outside of the can. This is what we call condensation, and it can mean big problems for computer components. Not only does condensation happen when using LN2, it happens profusely. If you poured a bit of liquid nitrogen into a container, the walls of that container would accumulate icy residue quite fast. This is why insulation is so important – it keeps the condensation to a minimum.

LN2 cooling should not really be considered Phase Change cooling, however, because it doesn’t really change phase in the same sense that most other Phase Change systems do. Most incorporate a rather complicated system of parts that alter a refrigerant back and forth between different physical states. At one point in this system, the refrigerant is extremely cold and can be used to absorb heat from components in your computer. I will describe this process in more detail later.

Another type of Phase Change system is the chilled water setup. In such a system, a standard water cooling loop is fixed with some sort of refrigeration unit that can rapidly cool the liquid being used to cool the components. This will allow the liquid to carry more energy and transfer heat away from your components much faster. Effectively used, refrigeration can cool your water to the point of freezing.