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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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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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  • $\begingroup$ So by using a higher pressure at the radiator and/or a lower pressure at the component, this would be possible? $\endgroup$ – Filip Haglund Dec 9 '13 at 16:16
  • $\begingroup$ @FilipHaglund - yes but you would have to do extra mechanical work - this is what your refigerator does. $\endgroup$ – Martin Beckett Dec 10 '13 at 5:02
  • $\begingroup$ So, a powerfull enough pump would work? With the correct radiator and block, that is. Thinking the pump does the mechanical work? $\endgroup$ – Filip Haglund Mar 1 '14 at 23:08
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i have pondered this theory before.

with ac the change in refrigerant state causes a high and low pressure range. when a car needs gas topped up its because the high pressure is not reaching the required pressure so when the state is changed it is cold.

if this would be possible with water would certainly interesting.

to throw another theory into the mix. an my appologies if how i think they work is incorrect.

The breathing air supply for sand blasting has a CCT, climet control tube, this tube has a single air supply, then inside the tube it splits the air, one sends air to the helmet, the other sends air out of a waste valve. by increasing the air flow out of the waste valve it will reduce the temp of the helmet 20degC. and vise versa.

Havent never pulled one apart i presume they work via the waste air passing the breathing air in a heat exchanger. one does multiple passes compared to the other single pass.

If anyone could find out the science behind these, they could add some possibilities into using water for a below atmos temp cooling system.

another note - air being able to absorb the most energy, aka heat, but needs physical control for this to occur. by simply increasing the air flow could this force the water temp lower than atmosphere.

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