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Stone as Heatsink
Stone as Heatsink
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Old 8th January 2018, 07:59 PM   #11
MagicBus is offline MagicBus  Greece
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This is αιγινήτικο κανάτι (Aegina's jug). It keeps the water inside it cool by vaporizing some through the ceramic body. Simple physics! Once, I thought how to use this as a heatsink but the drawbacks are humidity and necessity to fill water all the time...
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Old 8th January 2018, 08:06 PM   #12
globalplayer is offline globalplayer  Germany
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What about milling a cavity into the stone and hide a heatsink "inside".?
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Old 8th January 2018, 08:41 PM   #13
PRR is offline PRR  United States
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Originally Posted by johnnyx View Post
...thermally conductive insulating ceramic washers used for mounting high voltage power devices.....
Very thin. NOT all that thermally conducty; not like metals. Advantage is real low electrical conductivity and high breakdown. A thin electric-gap, not a heat spreader.

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αιγινήτικο κανάτι ...
Yes, evaporation is effective *after* you spread the heat over a large area to get a lot of evaporation. A jug of water is naturally large. Power chips, with present production economics, are invariably "small".

Small engines used to be evaporative cooling. Just an open water jacket. For a short run, the specific heat of water would absorb some HP-Hrs. Longer run, water gets hot and there was some evaporative cooling. Keep running, water boils away, you get a LOT of cooling but the water consumption may be high.
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Old 8th January 2018, 08:47 PM   #14
scottjoplin is offline scottjoplin  Wales
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If you had a slow dripping tap over the hot rock it would double as a sauna
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Old 8th January 2018, 08:51 PM   #15
globalplayer is offline globalplayer  Germany
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Originally Posted by scottjoplin View Post
If you had a slow dripping tap over the hot rock it would double as a sauna
Only if the silicon won`t melt before the stone is hot.
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Old 11th January 2018, 07:17 PM   #16
chrisb is offline chrisb
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so, the consensus so far?
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Old 11th January 2018, 08:10 PM   #17
GoatGuy is offline GoatGuy  United States
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Originally Posted by chrisb View Post
so, the consensus so far?
Yes.
Don't use stone as a heat sink.
Aluminum, or copper, or both esp. with water cooling of chips.

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Old 11th January 2018, 08:46 PM   #18
CharlieLaub is offline CharlieLaub  United States
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Originally Posted by chrisb View Post
so, the consensus so far?
Let's review why a stone heatsink would be a bad idea. Your transistor is a concentrated heat source, that is to say it is making a lot of heat in a small space. You need to transfer this heat away as fast as possible to keep the die cool. The total rate of heat transfer is dependent on the contact area and delta-T at the interface, and the thermal conductivity of the "sink" material. Since the area is small, you must have high thermal conductivity to keep delta-T down. Since stone has relatively low thermal conductivity, if it was used as a heat sink the delta-T would be high, meaning your transistor would be able to generate heat faster than it could be removed thru the contact are with the "sink". It would soon heat up and fail.

If you really want to use stone, you could first transfer the heat into a metal plate, and then from the plate via a large contact area to stone, which could then transfer the heat to air, also via a large contact area. But why do that when you can just use a finned aluminum heat sink to begin with? When sized appropriately it works very well, is robust, easy to obtain and fabricate, and is relatively inexpensive.
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Old 11th January 2018, 09:04 PM   #19
oohms is offline oohms  Australia
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You could try mounting your output devices on a thick aluminium L plate, then mounting that plate to a milled flat section of stone to try it. Don't forget to use thermal grease between the aluminium and stone.
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Old 11th January 2018, 09:12 PM   #20
scottjoplin is offline scottjoplin  Wales
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Was the OP serious? He hasn't been back. Is anyone else here serious? As well as getting a very smooth and fine contact between surfaces so as not to use too much thermal grease whose only function is to eliminate air gaps, pressure is the other important factor in thermal transfer, how are you going to attach the aluminium to the stone tightly without it cracking due to expansion and contraction?
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