aluminum heat sink in ottawa

[jon1985]

I am getting ready to make an few led fixtures but would rather buy the heat sinks localy to avoid crazy shipping.

Any ideas?

[Canoe]

Not enough volume locally to have competitive suppliers locally.
If you have some basic knowledge of heatsinks and heat exchangers, you can make your own, and save significant money if you get scrap aluminum.
If you don't mine eclectic designs, you can scrounge heatsinks from TVs and such left by dumpsters (watch out for the capacitors, some can pack a real wack).

[Canoe]

If by "LED fixture" you mean an array to cover the "foot print" of the top of the tank, then there are some options.
You need to get heat away from the LEDs.
You need to heat your tank.

* If your main fixture was a sealed box, the size of the "footprint", the LED assemblies could be mounted to its underside, electrically isolated from the box but thermally connected by TIM (thermal interface material) material. Not paste that may drop into the tank, nor epoxy that leaves you rather committed in your mounting, but TIM much like double sided tape.
* The sealed box will be a large flat-plate heat-pipe. If the box was 2" high, you'd put a 1/2" of deionized water in it, then have a valve to suck the air out of the box.
* As the heat transfers through the box bottom and heats the water, convection in the water means that the coolest water goes to the bottom to provide the fastest heat transfer possible by the water's temperature. Latent vapour pressure transfers the heat in the water to the coolest place in or on the box. This would normally be the top of the box, where the vapour will condense and fall back to repeat the cycle.

Construction of the box.
*Aluminum will provide for excellent heat transfer.
* It will need to be painted to protect it from corrosion.
* To maximize it's ability to radiate excess heat away from its top, you need to have the aluminum top lightly/wisk sand-blasted with the coarsest "sand"/media available (coarsest sandpaper is a distant second choice). This is to provide the roughest surface to maximize the actual surface area available within its footprint.
* This rough surface also has to be painted, but too thick a coat will fill in many of the nooks and crannies that are maximizing the radiating area. Paint in a spray-bomb/rattle-can can be sprayed into the air above the surface (not aimed at it as usual) and the fine droplets will float down and this "overspray" will lightly coat the surface. This ensures you do not have a wet surface that will self-level and fill in the nooks & crannies. The droplets will also provide additional radiating surface texture.
* Use matte paint. Engine enamel or caliper enamel with ceramic particles in it work well to aid heat radiation. If at all possible, use white paint. Yes, I said white. Not black. Black body radiation works well theoretically for a smooth flat surface, but in the practical world you want white paint for this textured application so the heat you've already radiated away is reflected away and not absorbed back into the textured surface it encounters. As NASA determined, a white textured surface gives you the maximum NET heat radiated away (gloss white in the sun, matte white in the shade).


To harvest this heat you'll be otherwise throwing away into the room, you can run a pipe through the side of the box looping above the water and exiting the box. As you run cool water through the pipe, the vapour inside the box condenses on the pipe, heating the pipe's contents. You'll have to figure out how to regulate getting this heated water into your system. Having a valve control whether tank overflow is heated or unheated on its return path to the sump is one thing to consider.
Another possibility is
* you are already pumping water from the sump up and into the display tank
* have a temperature sensor in the sump valve switch on/off a portion of that pumped water being diverted to the heat-absorbing-pipe routed through the box and gravity flow back to the sump, where this heated water mixes with the sump water to raise sump temperature
* this method doesn't require an addition pump to run, only a control voltage, temperature sensor and a valve

[jon1985]

sounds like a cool idea.