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I was just curious how much of a difference having the fins makes in a heatsink vs just a large block of metal.

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While the short and simple versions provided below are correct, this is a big enough subject in general for mechanical engineers to spend two semesters on... – dmckee Jul 15 '10 at 19:16
up vote 13 down vote accepted

The heat radiates from the surface of a heat sink, so the greater the surface area, the better the heatsink. Roughly speaking, if you cut a load of slots in your big block of aluminium, you could end up with, say, 5 times the surface area, and the heatsink can then get rid of 5 times the heat.

Have a read of the Wikipedia article - the big block is, in general, rather poor compared to the fins.

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+1 for the link. – steve.lippert Jul 15 '10 at 19:04
Oh for a giant copper serpinski sponge... – Everett Jul 25 '12 at 20:27

Fins give you more surface area for cooling, a large block has less surface area and would still have a hotter center than something that can get air right to the center of "the block".

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