Copper has very high thermal conductivity, which means it's good at moving heat from one place to another, useful if you have too much heat in one place (i.e. for cooling applications) or you want to add more heat to something (i.e. in cooking applications). Hence the popularity of copper in heat sinks, like this one intended to cool computer CPU chips, and in cooking pots.
This cool-looking heat sink was sent to me by a kind reader in August 2006, but due to my being very busy trying to finish the next version of Mathematica, I had a huge backlog of samples to photograph and it wasn't until January 2007 that my new photography assistant Nick Mann was able to get to this one. (That is how busy I am: I don't even have time to do my hobby, I have to hire someone to do it for me.) Amazingly, the kind reader emailed me asking when I was ever going to get around to photographing the sample he had kindly contributed, about two hours after Nick had finished processing it. After a five month delay, that's pretty good timing!
Anyway, back to the sample. It has a fairly thick slab of copper on the bottom, the side that will be in contact with the chip. (Typically you would add some heat-conductive cream to the gap to ensure good contact.) Sticking up from the slab are copper fins that carry the heat up into the stream of air generated by the small fan in the back.
Because the thermal conductivity of metals is typically goes up with higher purity, and because this is obviously a good-quality heat sink, I'm going to assume the copper in it is fairly pure.
Source: Dudley Fox
Contributor: Dudley Fox
Acquired: 20 January, 2007
Text Updated: 22 January, 2007