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A Few Thoughts On Cooling By Air Or Liquid

Last response: in Overclocking
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January 14, 2006 3:29:57 PM

It would be advisable in general to keep in mind natural convection heat flow when looking at cooling your rig. Since heat rises naturally, any case that is cooled by blowing air in at the top is not a good idea. The same principle that helps a fireplace work well applies to case cooling. When the flue of a fireplace fills with warm air, the rising air draws more cool air in the bottom. Forced cooling using fans should be set up to aid the natural convection flow of heat for higher efficiency. This is true also for liquids.
Warmer water or oil will rise to the top of a tank. bringing in the cooler water at the bottom of a case and letting it rise up and out the top will be more efficient and will provide a higher efficiency. If you are playing with the oil, adding an aluminum heat sink to the opposite wall from the board as in the featured article tests will cause the oil to circulate in the case and improve cooling. A similar effect is used on utility transformers where you see ribs or pipes sticking out the sides of the tanks, they create cooling oil fins that naturally circulate the oil.
As an electrical desig engineer in the transformer business, I have worked with some smaller oil cooled transformers. There are high tech oils used in some of the larger utility transformers but smaller ones typicaly use mineral oil as a coolant. It is lower viscosity than motor oils and won't suffer problems you will find with vegetable oils like oxidation from exposure to air and drying to the greasy goo you sometimes find around the caps of vegetable oil cans. Although it has not been tested (to my knowledge) on a computer board, it is of the highest dielectric strength and a good conductor for heat.
After seeing a few unique set-ups, It occured to me that you could possibly build a cooler using the water cooling parts and a home made heat exchanger from copper refrigerator tubing made to your custom taste that will act as a condenser and run isopropyl alcohol as a cooling medium. It has an excellent cooling characteristic and if it leaked, open the wndow and it will evaporate away (as a preferred medium to water) and it is relatively cheap and available at any drug store.
January 14, 2006 8:59:29 PM

its true the hot fluids rise to the top, however, in an enclosed ciruclating water loop, the temp difference is too miniscule to consider that theory. instead try to orient your loop so that it fits your case and uses the shortest amount of tubing - even if it means placing the radiator on top.

another thing is that mounting your fans on top or bottom really has no real world application because that 12 inches difference of elevation has really no temperature differences, so that logic doesnt' apply here

lastly using isopropyl alcohol instead of water is an option, however, it is much more dangerous than water it self. the isopropyl alcohol is widely used in water chillers for a lower freezing point
January 17, 2006 6:27:19 AM

The normal boiling point of ethyl alcohol is 78.5oC, although still high, i'm sure it would be a bad thing if the coolant in your system began to boil.
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Anonymous
a b K Overclocking
January 17, 2006 7:04:17 AM

Why would you want to use anything but water? Water has BY FAR a bigger heat capacity (equals cooling capacity) than ethanol or isopropanol, isn't flamable and doesn't dissolve plastic. Isoprop would dissolve your tubing; just trust me on these facts.
January 17, 2006 4:35:31 PM

Quote:
Why would you want to use anything but water? Water has BY FAR a bigger heat capacity (equals cooling capacity) than ethanol or isopropanol, isn't flamable and doesn't dissolve plastic. Isoprop would dissolve your tubing; just trust me on these facts.


lessons learned? ;) 
Anonymous
a b K Overclocking
January 17, 2006 5:41:23 PM

I just want to make sure...

You agree kumana1? (you reply could be misinterpreted...)
Anonymous
a b K Overclocking
January 17, 2006 6:03:12 PM

Just one other thing.

Imagine your 2-propanol dissolving your tubing. It wouldn't spill all over the place in the beginning. Fumes would leak into your casing, mix with oxygen and then create a perfectly explosive mixture (flash point=12C and explosion limit from 2% on). Next time you turn on your system... Just imagine a small granade exploding next to you. Followed by a nice little and hard to extinguish fire.

While isoprop and other solvents might be used in very specialized equipment, your computer and generally your home electronics environment isn't the right place for experiments like that. Leave that to pros and nutcases. The nuts will be easy to spot; The newspaper. obituary notice.
February 10, 2006 5:10:54 AM

lol glad someone mentioned that alchohol is uh FLAMMIBLE! I don't want to be anywhere near that pc when it's powered up.
February 10, 2006 5:27:37 AM

I don't think alcohol is such a good idea. Explosive pc doesn't sound safe.
!