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How does sub-ambient cooling work?

There are water cooling systems for computers that can cool components to below room temperature. The problem I see here is that the water is cooled using room temperature air. How can the cooling system keep a 150 watt computer component at a temperature below room temperature? The only powered device on the water cooling loop is the pump and since that isn't being cooled by anything else than the water it cannot contribute to the lower temperature.

I'm guessing this has something in common with a Geothermal heat pump, but reversed.

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1 Answer 1

up vote 4 down vote accepted

Assuming the cooling system is just a radiator, water and a pump then you can't cool the fluid below the ambient temperature of the radiator.

A refrigerator manages this by compressing the fluid in the cooling circuit, extracting the excess heat and then expanding it to make it colder. If your system uses a phase change, a compressible fluid or a peltier stack it is a refrigerator

edit: possibly if you evaporated some of the water you could cool below ambient. But you would need an unlikely combination of relative humidity and water temperature and would extract very little power. And anyway this would be a refrigerator

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So by using a higher pressure at the radiator and/or a lower pressure at the component, this would be possible? –  Filip Haglund Dec 9 '13 at 16:16
    
@FilipHaglund - yes but you would have to do extra mechanical work - this is what your refigerator does. –  Martin Beckett Dec 10 '13 at 5:02
    
So, a powerfull enough pump would work? With the correct radiator and block, that is. Thinking the pump does the mechanical work? –  Filip Haglund Mar 1 at 23:08
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