The idea is to create a hand-crank food warmer. The heat is created by friction from the rotating crank.
I imagine this could be done in one of 2 ways. It could either be a home appliance that looks something like this:
or it could be a small-form, portable version that is made from 2 components:
the hand crank, similar to the one featured in the header image
A flexible band filled with oil similar to this:
You wrap the band around the can or whatever you want to warm up. Then start cranking. The heat from friction is transfered to the oil which circulates through the band and back into the heater.
You could use it to heat anything. The band just has to be long enough to wrap around stuff.
This was inspired by Samuel's idea.