Thermoacoustic Refrigeration

Thermoacoustic fridges are magic: you heat one end, and the other end gets cold. (Of course you have to sink all that heat from the middle.) They can easily be made long and skinny, and so are a natural for use down drillholes. They're also made entirely of metal, and have no moving parts, so they will survive bouncing around in the back of a truck.

This was a design study for a general purpose fridge for 2-inch cased holes (38 mm maximum OD) that would solve many of the temperature problems of downhole operation for a wide variety of sensors.