A race of beings decides over a few pan-galactic gargleblasters one evening that rather than waste scientific minds on developing hyper-advanced technology, they should just build a huge computer to design clarkean devices for them. A computer of this size naturally requires a huge power source, so this is what they come up with:
An enormous spherical computer is built, consisting of trillions upon trillions of densely-packed processors each the size of a brain cell. This processing layer surrounds a huge reservoir of water. The computer is placed in orbit around a large body such as a gas giant, and due to tidal flexing, the fluid heats up.
The difficult part: I had originally planned for the hot water to be channeled up from the core, turned into steam and used to drive fans and so power the processing layer, until I realised that this would then involve venting the steam into space, and thus slowly depleting the core of fluid. So, is there another way to produce a giant supercomputer powered by tidal flexing?