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Originally Posted by cloasters I thought that water cooling was more effective until I read Kaitain's learned post. Is it safe to posit that even at 15C above room temperature, water still removes heat noticeably better than air cooling? I'm asking about the huge gain in efficiency by using dense water as opposed to nebulous air. |
Yes. Using water is hugely advantageous over using air, mostly due to the fact that water can "absorb" (sorry engineers) more energy per degree celcius it warms up than can air. A lot more. Which is handy
With water cooling you can also be a lot more flexible. The approximations I have outlined above are only approximations, and rather conservative ones at that. I have actually based them on the API standard "short cut" designs for air- and water- cooled heat exchangers. As you're aware, from the first law of thermodynamics, heat "flows" from a hot place to a cold place, but not from a cold place to a hot place (unless energy is provided to drive it - 2nd law). The rate at which heat is "driven", so the number of Watts transferred is directly proportional to the difference in temperature between hot and cold side.
There are better performing blocks that manage approach temperatures of only a couple of degrees celsius, and there are ludicrously oversized, overfinned and overfanned radiators which hold the water resident for so long that it returns to almost ambient temperature. These are at the extreme end of the "normal" scale. You'll find you get very far beyond the point of diminishing returns if you aim for one of these.
For reasons I'm happy to explain later, the point that makes the most difference in a cooling loop is the transfer of heat to air (radiator). It's the slowest step and so determines the rate at which the cooling loop ultimately transfers heat, so the temperature of your CPU.
For people who live in the desert, this causes a problem as your CPU will roast, toast and generally fry eggs unless you help your cooling loop out a bit. What you need is to increase the temperature difference between the water and the air to a huge number, without making the water too hot for the CPU. Two ways have been traditionally used here:
1) Peltiers,
2) Refrigeration
These exploit the principle of heat engines - pumping heat from the cold side to the hot side. Consumes energy so the 2nd law isn't violated.
With a peltier, the hot side is cooled by the water, raising its temperature to something stupid (60ºC e.g.) Then you've got a temperature difference between water and air of more like 35ºC in a normal temperate climate, and a reasonably well designed radiator should dissipate 25ºC of those. In reward, the cold side of the pelt can easily achieve temperatures closer to 0ºC
With refrigeration, such as whatever's using, exactly the same system works. Wave your hand near the radiator of your fridge. Don't touch it, because they can be VERY hot, and you'll see what I mean.
The difference is this: with the first set up - a standard water loop, heat is being transferred simply by allowing it to flow from the hottest point to the coldest point. With the latter set ups, heat is being actively pumped from a colder point to a hotter point, the better to dissipate it to air.
If you're expecting miracles out of the first, you'll be disappointed, however it is still more effective than relying on a lump of copper, air and an 80mm fan.