metalman2785

I originally made a thread describing the physics behind extreme cold and overclocking, but now that the FAQ section is up so I decided to post this in the FAQ's section where it belongs.

As most of you know colder temperature, especially extreme cold, is very beneficial for overclocking. I am now going to explain why this happens from a Material Science standpoint.

First Equation that you need to understand is Ohms Law.

1. Ohms Law states that: V=IR

Where V is voltage, I is amperage, and R is resistance. Higher voltage means more amperage or less resistance.

A step up from this equation is the resistiviy equation. Resistivity is a mechanical property, different than resistance. The relationship between resistivity and Resistance can be seen in equation 2. Resistivity is dependent on Temperature, resistance is not.

2. R = P L/A

In this equation P is going to be resistivity, R is resistance, L is length (such as length of a wire), and A is cross-sectional area (of a wire). We can see that as P (resistivity) increases The resistance will increase. A longer length (L) of wire will also increase Resistance.

The final equation to tie this all together is the conditions effecting resistivity. There are 3 major things that will determine the resistivity of a material. They are temperature, impurities, and deformation.

3. P (total) = P (thermal vibration) + P (impurities) + P (deformation)

P(total) is the total resistivity, and the other P's are the factors of resistivity. This equation shows that the higher the temperature, the more thermal vibrations will occur, thus causing a higher resistivity. At extremely cold temperatures such as -100 C the thermal vibrations of the atoms will be much smaller then at room temp. These smaller vibrations translate into a loss of less kinetic energy. This means that effiecency is greatly improved at cold temps. You will get a higher overclock with less voltage at these extreme temps. The other two factors, impurites and deformation also play a role in resistivity. A high purity copper with a mirror finish will have low resistivity.

Well I hope this helps explain why cold temps are better for overclocking, note that some electrical components such as capacitors will fail at extreme cold temps. It has been observed that in some new chips the memory cotroller tends to stop working properly at cold temps, this is known as a "cold bug". Also these equations only apply to electron flow in metals, seimi-conductors or ceramics may be different. Peace!

COLTCOMMANDO

Cold=better Ok i got that. makes sense

E=Mc2xPie/|"%^ i got a "D" in science, you must be a teacher. This totally doesnt help your average bear

Edit: My brain froze

Kahuna513

Thanks, helpful, and tells me all I need to do this piece of Science Coursework on Resistance in a wire. lol

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Johnny Quest

Thanks, you have open a line of discussion that I have thought about before. Maybe you can help. I have always wondered why there are not more CPU coolers being sold besides air & water. Why not freon ?

What would happen if you immersed a CPU in liquid nitrogen ?

How much faster could you run a typical over-clockable CPU then ?

Has this been done ? I'd like to read about it if so. Images, etc... if anyone knows.

TIA,

Johnny

metalman2785

Liquid Nitrogen and Dry Ice have been used for a while to extremely cool cpu's for a major oc. Also single and multi stage phase change units are used to cool cpu's, some commercial ones are Vapochill and Prometia. They don't use freon because it destroys the ozone, most of the phase change units use refridgerent R407.

JJ_3

hah..thats pretty neat..i was just thinking..if u put the cpu in liquid nitrogen..and all the heat..well..idk..couldnt it crack or something? lol

metalman2785

The CPU isn't imersed in liquid nitrogen, instead a copped container holding the LN2 is placed over the CPU and gets it down to -100 or more deg C. The cpu won't crack, but condensation becomes a major problem and the mobo and cpu need to be insulated and covered in a dielectric grease.

JJ_3

O LOL well that makes a little more sense..but still..burrrrrr how much more did them people get out of their cpu?

metalman2785

Well for example an AMD FX, depending on the stepping, may be able to run at 3.5-3.8 ghz at these extremely low temps. An 3.7 Intel EE would probably be able to run at 6.4 - 7 ghz depending on the chip. Basically these speeds would not be attainable without these extremely low temps. All of the 3D and super pi world records will use either Dry Ice,Liquid nitrogen or a multi-stage cascade (refridgeration cycle) to reach these very low temps.

youngmoney

overclocked with liquid nitrogen

http://youtube.com/watch?v=AdbsnEYr0...elated&search=