Why can't i cool my CPU with dry ice?
Cooling your CPU with dry ice does not sound like a good idea. There are many problems associated with this technique.
1) Dry ice has to be bought, stored, and handled very carefully. It doesn't last all that long (it sublimates, boiling off carbon dioxide constantly). You can't touch it with your hands (wear extra-thick gloves, and keep water away!). You may be able to get some at ice-cream shops, but the cost may add up to more than $100 if you run your computer a lot like this.
2) You constantly have to add more dry ice -- it sublimates away all the time. Depending on the size of the chunk you put in your computer, you may have to replace it every few minutes. A 2.2 GHz Pentium 4 (a typical modern processor) dissipates 57 watts of thermal energy. The latent heat of dry ice is 590000 Joules per kilogram, meaning you'd go through the stuff at a rate of about a pound an hour. Overclocking only speeds this up. And it absorbs heat from the air and surroundings, not just the processor, so it disappears even faster.
3) In a humid environment, the dry ice will frost up. Water vapor will condense on the block of dry ice and make regular ice. When the dry ice sublimates, this stuff falls on your processor and motherboard, making it wet. Even just cooling off the components of the computer below the dew point will cause water to spontaneously condense on your computer parts. They may not work when wet (short circuits!), or the water may speed the corrosion of electrical contacts.
4) You need good thermal contact between your dry ice and the processor. Dry ice when it changes into a gas, makes a thin cushioning layer of escaping carbon dioxide around it. This acts as a thermal blanket, keeping more heat from traveling to the ice. You can push the dry ice against the CPU, but what will happen then is that you will get vibrations. Vibrations tend to shake electrical contacts loose.
5) Speaking of electrical contacts, cooling a portion of your computer down to very low temperatures and not others will create mechanical stresses in your computer parts (most likely in your processor). When stuff cools down, it shrinks, and when it heats up, it expands again. Cooling down only a part of your computer makes that part too small to fit nicely into the other parts. You may crack something or, more likely, just break some electrical contact somewhere. Small electrical components can be fragile!
6) You have to make sure not to run out of dry ice -- if you run empty, the processor will overheat very rapidly and stop working.
Water cooling is difficult -- you have to make sure there are no leaks and no vibrations introduced by pumps. It is (was) often used for large mainframe computers, but is not common on today's smaller units.
Our suggestion is to get a good heat sink and a fan. There is no limit to how much heat they can carry away -- air comes in for free, and the fan and heatsink are not that expensive (your computer probably already came with one, but you might want to get a better one). You may want to look at heatsink roundups on computer-related websites, but be forewarned about the quality of information you may find on the web. You can also slow down the processor again. Usually you can get more performance out of a computer by buying one later, as processors get cheaper and faster all the time anyway, and overclocking is just a really hard way to go about this.
-Jeff and Tom