I had a pair of those flex metal eyeglasses, the type you can wrap around your finger and they spring back.
I noticed one day that when you bend the metal it gets hot, and after you release it, it becomes cool .
If you had a band of this stuff rolling over some pulleys like a belt, you could generate a cool side and warm side, like the coils in a a/c unit. But I expect the cop wouldn't be too great though.
Not really a practical idea, but I never heard of using a solid (chemical reactions excluded) as a cooling medium.