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Koolance CPU-LN2-V2 Liquid Nitrogen Pot

Posted August 2, 2010 by Jake in Cooling







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by Jake
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Extreme Cooling 101

In order to understand the implications of a liquid nitrogen pot such as the Koolance CPU-LN2-V2, we first need to understand the background and basics of extreme cooling. First off, a bit of chemistry.  I promise this will be brief and simplified. 

There are generally three substances you would normally use in a sub-zero pot for cooling a CPU: dry ice, liquid nitrogen, and liquid helium.

Dry ice is often referred to as DICE by enthusiasts, and is carbon dioxide (CO2) in solid form. Perhaps its most interesting property is that it doesn’t melt; it sublimates.  That is, it converts directly from a solid to a gas at -78.5°C, so it literally vanishes into thin air as it is consumed during a benching session.  Dry ice can be readily found in most geographic locations.  It’s relatively inexpensive, easy to store in an insulated cooler, and comes in various forms such as blocks or pellets/nuggets (the latter is best for use in a cooling pot). 

However, dry ice needs a liquid medium for use in overclocking in order to take advantage of the low temperatures; you cannot use water, for example, because it would freeze. So the trick is finding a liquid that will cool to a very low temperature. Many people will suggest using acetone but frankly, acetone is nasty stuff with a litany of potential safety and health risks; suffice it to say it’s to be used with caution.  I prefer using Methyl Hydrate instead with dry ice. It’s not exactly the safest substance out there either, but I consider it the far lesser of the evils. It can be found at any hardware store, it’s cheap, and it works just as well as acetone but doesn’t stink up the entire room, and you won’t faint with decent ventilation.  In any event, dry ice is great for sub-zero beginners due to its ease of use, low cost, stability, and ease of storage (though for only short periods of time).  You don’t even really need a sub-zero thermometer since the temperatures don’t vary much as long as you keep dry ice topped up in the pot; DICE stays at a stable temperature and all you have to do is top it up once in awhile when it gets low.

When using dry ice, you will need a glove for the hand that comes into contact with the pellets. Prolonged contact with bare skin can cause frostbite. Some people prefer to use a small wooden or plastic spoon to scoop the nuggets into the cooling pot rather than handle them directly with gloves. Either way is fine, but exercise caution; do not use any sort of metal spoon. Brief contact between dry bare skin and dry ice won’t hurt but if your skin is wet or sweaty you could run into problems. Think of the dumbass who licks a frozen metal pole in the winter; well, dry ice is far colder, so the dangers can be as well. You get the idea.

The second substance normally used in a pot is liquid nitrogen.  This is what the big boys (and girls on occasion!) use for extreme overclocking.  Liquid nitrogen, often referred to as LN2, is a liquid that maintains a temperature of approximately -196°C.  The interesting property of LN2 is that it boils away into thin air at temperatures far colder than what dry ice would reach; it literally evaporates away when it hits a warmer substance.  Liquid nitrogen requires an expensive, special container called a dewar for storage.  Sourcing LN2 is more difficult than dry ice, and it is more expensive. 

Because it is far colder than dry ice, LN2 is more effective in cooling a CPU and thus reaching higher overclocks, but it is also far more difficult to work with.  LN2 boils away quickly and regular pouring and temperature monitoring is required to maintain stable temperatures.  Liquid nitrogen is more appealing to the hardcore enthusiast, but it is also more expensive, more dangerous (in terms of sheer low temperatures and pressurization issues), and requires specialized storage and a separate pouring container, as well as more patience and more nerve when used for benching.

Due to the extreme cold of liquid nitrogen, extra caution must be used when handling or transferring it. Insulated gloves are recommended, and a vacuum sealed, double-walled pouring container is needed for topping up the cooling pot. It must be stored in a dewar though. A dewar is a specialized tank to store liquid nitrogen. Since LN2 expands to several hundred times its volume when going from a liquid to a gas, you cannot store LN2 in a sealed container; the damages could be serious. As a result, a dewar is not only insultated for cold, but also vented to avoid pressure buildup. Dewars comes in various shapes and sizes (and price ranges). Below is what one type of dewar looks like:

As liquid nitrogen boils off (either when pouring out of the dewar or in the cooling pot itself), the gas is also cold, unlike the gas sublimating from dry ice. However, there is an interesting upside of the extreme cold of liquid nitrogen: when used safety it can do some amazing things, such as freezing a strawberry in about 5 seconds flat, for example. But probably one of the most fun things to do is make liquid nitrogen ice cream. Rather than using traditional methods to turn the mixture into a solid, the very rapid freezing from LN2 avoids water ice crystals, creating what some people say is the best ice cream you’ll ever taste. And on a side note, trying to impress the ladies with your mad LN2 pouring skills during a benching session probably won’t go over so well, but liquid nitrogen ice cream definitely will.

And lastly, liquid helium is also used in a sub-zero cooling pot.  Often referred to as LHe, think of it as LN2 on steroids.  Liquid helium maintains a temperature of approximately -269°C.  Reserved for only the most diehard enthusiasts, LHe is very expensive, very difficult to source, and extremely cold.   It also requires specialized storage and constant monitoring similar to LN2 when benching.  LHe is also normally used only on CPUs that don’t have a cold bug, which is why we see LHe predominantly used on AMD Phenom II processors. LHe is generally reserved for only the most talented and hardcore overclockers; frankly if you can get, afford it, and use it, then you aren’t reading this review because you’re already an expert.

Regardless of the sub-zero method you choose, always understand and follow proper safety practices.  Each of the substances described above have inherent dangers due to their extreme cold nature, as well as pressurization issues in the case of the liquids.  Always be sure to exercise caution when using these substances to avoid safety issues.  Don’t bench when you’re tired or distracted; stay mentally alert and sub-zero overclocking can be very fun and exciting when done smartly.

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