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post #34 of (permalink) Old 07-14-2019, 02:47 PM
Asmodian
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Quote: Originally Posted by opt33 View Post
Im sure air at 0.024 W/mk thermal conductance doesnt need much surface area just like water at 0.6 w/mk doesnt need much surface area when cooling hot spots on die. Traditional thinking of a large copper air cooler spreading heat instantly at 400 w/mk to 1000's times surface area via fins before attempting to transfer heat at a very slow pace of 0.024 W/mk for air... that is all nonsense, just like waterpins/channels doing same for waterblocks is all nonsense.
You seem to only be thinking of water and air as static thermal transfer materials. This is wrong. You are not using the water to transfer heat to something else, you are heating up the water directly. If you tried to simply cool the CPU with a static water bath it would not work very well (convection would allow it to work much better than the 0.6 W/mK would suggest, but still not very good).

Air has very little thermal mass to heat up and has a low heat capacity per mass, so it is incapable of absorbing much heat energy. Water is much better at absorbing heat and jetting it into the back of the core allows it to absorb the heat directly, not needing to transfer it. This is why the jets are important in all water blocks.

Per volume air has about 0.0153% of the ability to absorb heat compared to water. Or stated another way, compared to air the same volume of water will absorb ~6500x as much energy when heating up one degree.

Quote: Originally Posted by prjindigo View Post
The truth is that even jets against the cooling plate don't work well because of turbulence and effect, once the jet leaves the aperture there's no guarantee of laminar flow and it just becomes a mess of cooled water mixing with hot water and all of it flowing sideways out of the system.
This is ideal, turbulence is desired to transfer as much thermal energy to the water as possible. Laminar flow requires a much higher surface area for the same energy transfer due to the boundary effect and the low thermal conductance of water.

Test is some time. If you hold your hand in a stream of cold water and compare how cold it feels when flowing the water along your hand parallel to the stream or with it impacting your hand directly, perpendicular to the stream. Especially significant (and relevant) when cooling a fresh burn.

Last edited by Asmodian; 07-14-2019 at 03:08 PM.
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