[Peter Wirasnik] has been casting his own aluminum heat sinks. He’s working on capturing the heat from a car’s exhaust system and turning it into electricity, kind of like the candle generator. In the photo above a standard heat sink is bolted to one side of a Peltier cooler with [Peter's] own casting on the bottom. That casting will connect to the exhaust pipe and transfer heat to the Peltier while the other heat sink keeps the opposite side relatively cool. What results is a voltage between 600mV and 1V.
We’re not quite sure what the end product will be but the casting process is fascinating. He carves the shape of the piece he wants to cast from Styrofoam and embeds it in a box of sand. He then melts salvaged aluminum in a cast iron frying pan using what looks like a propane torch. Once molten, he pours the aluminum into the mold and it burns away the Styrofoam as it fills the void. A little cleanup and he’s got the heat conductive mounting bracket he was after.