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Old 06-29-2010, 02:10 AM   #1
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Question Aluminum Thermodynamics? Thickness for a heat spreader?

I am making a large LED setup and I was wondering if there is much difference with heat transfer going from 1/4" to 1/2" thickness. On the underside the LED's are attached with thermal paste on the top is copper pipe screwed on with thermal paste to help fill the gaps. (water running in copper pipe to cool the aluminum slab.)
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Old 06-29-2010, 03:40 AM   #2
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The thicker the better. Aluminum has a very low specific heat: It dissipates and absorbs heat very easily. Specific heat is measured in units of joules/g-kelvin. In otherwords to raise a gram of aluminum 1 degree kelvin you would nee X joules. Now if you made your heat sink a small mass it would take a smaller amount of heat to raise it 1 degree. But if you had more mass you would have to generate more energy to make it the same temperature. Thus I would suggest the thicker plate.

Remember: Air is a very good insulator, that's how fiberglass batting works, it traps air inbetween threads of glass which is also a moderately decent insulator to prevent the movement of energy, heat, so the more energy your aluminum can absorb before heating up the less likely it will over heat your bulbs.

I know there is a slight volume to surface area gain with the 1/4" plate but that is nullified as there is so little surface area.

The optimal layout I think would be a 1/2" aluminum plate with copperfins spanning lengthwise across it at 1/4inch intervals with 6x 120mm fans blowing across it for your set up. The 320g right? The design I've proposed is basically a scaled up model of a cpu cooler.
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Old 06-29-2010, 05:08 AM   #3
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Peltier anyone? Those are probably the best you can do without actually expanding liquids and such, but one side of it will get really really hot, the other side will freeze, and they aren't very efficient :P
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Old 06-30-2010, 10:11 AM   #4
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Heat sinks are as much about surface area as anything else. With a water-cooled setup like yours, it's best to place the LEDs as close to the water as possible, so go with the thinner aluminum. The aluminum and copper are really just acting as heat conductors. The water is doing the real cooling work.
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Old 06-30-2010, 11:26 AM   #5
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Greenmaster, How big is the water reservoir on the liquid cooling system. You realize you still would need to dissipate the heat out of the water somehow.
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Old 06-30-2010, 06:38 PM   #6
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Hmmm, too bad he couldn't use his tank water for the water to cool it. Basically it'd be acting as the heater, then when the tank got too hot a solenoid would kick on and the water would go through a small oil cooler (small radiator) with a fan attached to it to cool it down.
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Old 07-01-2010, 12:47 AM   #7
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Hmmm, too bad he couldn't use his tank water for the water to cool it. Basically it'd be acting as the heater, then when the tank got too hot a solenoid would kick on and the water would go through a small oil cooler (small radiator) with a fan attached to it to cool it down.
I'm using copper pipe for heat conductivity... so no tank water mix... but that gives me an idea.... Thanks... I'll keep you posted if I can find out a way to make it work... but that would go away from the motto KISS (Keep It Simple Stupid) we will see.
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Old 07-01-2010, 12:49 AM   #8
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Greenmaster, How big is the water reservoir on the liquid cooling system. You realize you still would need to dissipate the heat out of the water somehow.
After the water has passed through the top and comes back to the basement I will route it underground (geothermal cooling) about 100 feet of pipe in 3 feet of dirt. (I hope that is enough to dissipate the heat.
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Old 07-01-2010, 02:45 AM   #9
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I'm wondering, did that mean that it would be 3 ft deep? I'm a little worried about it freezing during the winter.

Also, would running pipes underground be more efficient than running radiator (heat sink+fan into air) Right now I'm thinking mud huts and insulation.
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Old 07-01-2010, 02:59 AM   #10
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I'm wondering, did that mean that it would be 3 ft deep? I'm a little worried about it freezing during the winter.

Also, would running pipes underground be more efficient than running radiator (heat sink+fan into air) Right now I'm thinking mud huts and insulation.
3 feet under ground... the frost doesn't get more then 3-6" down, and running pipes under ground you only have to run the pump there is no fan. In the summer as well it helps to keep the heat out of the fish room.
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