Aluminum Thermodynamics? Thickness for a heat spreader?

[Greenmaster]

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.)

 

[Crepe]

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.

 

[krap101]

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

 

[BigJim]

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.

 

[Crepe]

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.

 

[corrado33]

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.

 

[Greenmaster]

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.

 

[Greenmaster]

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.

 

[krap101]

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.

 

[Greenmaster]

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.

 

[krap101]

This kind of stuff interests me, and I think the phrase that keeps coming up is thermal mass. I'm wondering, if the leds get hot enough, during the day the setup will cool the lights/heatsink (the ground is still cold from the night before) but during the night, the ground will begin to add heat to the system, but then again the lights will probably be off during the night? Soil isn't a very good conductor, and it would seem you are trying to delay the effect of the heat until you can turn your lights off?

 

[BigJim]

The frost doesn't get below three feet in Canada?!? Here in Chicago we have to bury pipes down five feet to prevent freezing.

By the way, this seems like major overkill for cooling an LED system. One of the biggest reasons to go LED is the lack of heat compared to the other popular lighting systems. Personally, I'd just get a big strip of heat sink and a couple fans.

 

[Greenmaster]

Canada is the biggest country in the world. We have winters that range from -40 F(-40 C) to some places that don't get much below 32 F (0 C) for more then a day or two. LED's produce similar per watt to a MH but most of the heat is at the base of the unit with LED's and MH tend to radiate more heat. LED's also produce similar light to MH (80 Lumens per watt is the LED's I'm going with) I also believe that "...a big strip of heat sink and a couple of fans." would not be adequate... I would need a bunch of fans and that adds noise which I don't need.

 

[Greenmaster]

This kind of stuff interests me, and I think the phrase that keeps coming up is thermal mass. I'm wondering, if the leds get hot enough, during the day the setup will cool the lights/heatsink (the ground is still cold from the night before) but during the night, the ground will begin to add heat to the system, but then again the lights will probably be off during the night? Soil isn't a very good conductor, and it would seem you are trying to delay the effect of the heat until you can turn your lights off?

That's why you need lots of pipe under ground. If you look at geothermal heat pumps for house heating/ AC you will see what it looks like on a large scale. At about 6' down the ground stays the same temp all year long and by the time the water gets back to the pump it has equalized with the ground, and the heat continually dissipates out from the pipe. I'm hopping that I can run the lights 24/7 and not experience higher temps coming back to the pump, because I plan of having my refugium lights on at night. If it is still warm when coming out of the ground then I will add another 100' of pipe under ground.

 

[Crepe]

I suggest using a mix of antifreeze and water just in case.

 

[Greenmaster]

I suggest using a mix of antifreeze and water just in case.

Thank you. I'm planning on doing that, but it's more because it doesn't just appear underground. It will be exposed for a foot or two.

 

[David S]

I would be very careful using water to cool your leds.when water is used and is constantly being heated and cooled within a closed loop you may get legionella in your water system which means chemical dosage aswell as a very dangerous situation for yourself and your family.Is it for the leds or the drivers you need the heat sinks for?

 

[Crepe]

I'm pretty sure a good dose of antifreeze would poison living things in there.

 

[David S]

antifreeze won't touch legionella ask any air conditioning engineer.

 

[Greenmaster]

It will be a closed loop system with copper pipe so I will not have to worry about it... also it's RO/DI water so there is nothing for the bacteria (if it does get into the system and live) to eat thus no multiplying numbers. Also the only way water to get out of the system is if there is a leak. On another note, I got my tank YAHOO!