GordonThree wrote:
westend wrote:
Hey Gordon,
From my experience with heat dissipation, I don't think you're going to get much better dissipation by increasing the dimensions of the aluminum plate. Heat from devices like this transfer from conductive to convective in a fairly small locality. You may get better reflectivity, though.
Nice polish job on that block!
You are correct, increasing the size of the plate alone does not help much with convective cooling. My goal is to increase the thermal mass. If the LEDs are heaters, running on a fixed power, the more mass they have to cool, the less heat will be "trapped" inside them. Entropy of the mass is always working to cool it... at least, that's the theory I'm working off of.
As long as I can keep the system under 200F with high ambient temps, I'll be happy. I don't have anything fancy like a FLIR camera, but I am going to get one of those laser pointer temperature probes.
If the big slab of aluminum can't keep things cool, I'll ditch the plastic fixtures entirely and go with a recessed heat sink in the ceiling. There's a new piezo-electric LED cooler I've been wanting to try. :)
Thanks for the comment on polishing, it's something that is tedious as heck and no one gives me a back pat because they can't see it. ;)
Your theory on mass and entropy are spot on. I should have worded my other post better in that devices dissipate their heat into the mass in a very localized manner. If we use a device that has 10 C/W and wish to dissipate the junction temperature to 50C, let's say, we would find that the greater amount of dissipation occurs within a radius of twice the devices area. Temperatures farther out than that fall off quickly. This is the conductive heat transfer and is the reason why a finned heatsink is more efficient, it increases the area where conductive and convective transfer interface. Sometimes a finned sink isn't the right one, though. You also have the mounting pad that is spreading heat. I think you'll meet your heat goals with what you have.
