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Couple of questions about thermal compound substitutes on GPU and about heat emissions/conductivity

post #1 of 3
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Okay, the stubborn here managed to remove all the thermal compound from his GPU, just before he realized that he had no other compounds lying around. Yeah, I ended up with a very hot GTX 580 on a very hot spring day (like really hot, 33ºC/91ºF) with no thermal compound. The GPU have a (shame on me) air cooling system. Recipe for a disaster. Well, after that I bought a Noctua NTH1 thermal compound online. It is going to take a while for it to arrive (about 4~5 days). I tried to use the computer with the poorly cooled GTX 580. 55ºC idle, 96ºC on 60% load, no OC. I didn't even tried 100% load, as it would have probably set to whole thing on fire and burnt my house, neighbors and probably the entire city on a very dramatic incident that would resemble a hydrogen bomb. I spent some time Googling on substitutes for the compound, and I found that aluminum foil would do the job quite poorly. I tried, and it managed to cool things down a little bit, but...Well, what about mineral oil? Would it perform okay for the next 5 days on regular load? Would it work better than aluminum foil? I also found something about silicon grease. I'm not sure about it though. How would it perform? Any other ideas?


Now let's move to general questions about heat:


While googling on thermal compounds, I came across people discussing if ethanol would do a better job on water cooling than water itself. Apparently the answer is no, because of something called heat capacity. I know that water have a high heat capacity, meaning (correct if I am wrong) that you would have to apply a large amount of energy to make the water's temperature rise in comparison with ethanol. But I don't get it: That means that ethanol absorves heat more easily than water, therefore it was supposed to perform better as fluid for a liquid cooling system, right? Can some one clarify that for me?
Edited by Guizin239 - 10/29/12 at 9:01am
post #2 of 3
OK,

Just a small thing here, there is a return key to the right of your keyboard, use it between paragraphs, it'll help people read the post. Now onto the other side of your issue. Do NOT try to use anything else as thermal paste, it's a bad and frankly stupid idea to try anything like that on the type of card that you have.

Wait until your thermal paste/pads come in and use that when you get it.

Comps

P.S By the way, ethanol has a lower boiling temperature than water which isn't good, it's also a corrosive and will damage the loop.

C
post #3 of 3
The high specific heat capacity of water would be what makes it advantageous over ethanol. To understand it you have to realise that Heat is just a form of energy, and temperature is not the same as heat. Temperature is an average measure of energy, whereas Heat is the total.

The specific heat capacity of Ethanol is 2.44 J / g / K (Joules per gram per Kelvin), the specific heat capacity of copper is 0.385 J / g / K. This means that Ethanol needs to absorb ~6 times as much heat as copper does to get an increase in temperature of 1K (1 Kelvin = 1 degree Celsius). Water's specific heat capacity is 4.1813 J / g / K, another ~1.75 times that of Ethanol and almost 11 times that of copper. This means that if ethanol were to cool the waterblock (which for simplicity, is solid copper) from 70C to 30C, a difference of 40, the ethanol would increase in temperature by ~6.6C (6.6K). If water were to do the same, it would only increase ~3.6C (3.6K), and so is able to take even more heat away from the water block.

Another way to look at it would be to say if the ethanol rises in temperature by 10C (10K), it's reduced the waterblock's temperature by ~60C (60K). If water rises by 10C (10K) it's reduced the waterblock's temperature by ~110C (110K).

I don't know much about water cooling but lower temps always sound better to me.
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Phenom II x4 955 BE ASUS M4A87TD-USB3 Powercolor Radeon HD6870 1GB 4x GeIL Value 2GB 1600MHz 
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