[Amps] Anodizing aluminum, painting etc.

[Peter Chadwick]

If you had a heat sink of zero mass, infinite conductivity and zero thermal resistance btween sink and air, it would work perfectly, no matter what size it was. So mass itself doesn't matter: the implication is that greater mass equates to greater area and lower thermal resistance. After all, which is going to give best results - 500 grams (OK, 1 pound in the US!) of depleted uranium or 500 grams (1 pound) of aluminium? The aluminium obviously has a greater volume, and thus a greater surface area.
In this imperfect world, the mass times the specific heat tells you how many calories are needed to raise the sink temperature above ambient by some amount. The power being dissipated at 4.2 Joules/calorie tells you how long it takes to do it. The Theta sink-to-air tells you how much heat the sink is losing. The complication then  occurs because the sink is not generally at equal temperature all over. In any case, all you're really interested in at the end of the day is Theta-junction-to-ambient. From memory, you can end up with set of simultaneous second order differential equations trying to work it all out from first principles, and those are things that I avoid!

73
Peter G3RZP