The document discusses heat pipes, which transfer heat using evaporation and condensation. Heat pipes work by having a container filled with a working fluid and wick. Heat is applied at the evaporator, vaporizing the fluid. The vapor moves through the container to the condenser, where it condenses and transfers heat. The condensed liquid is drawn back to the evaporator through capillary action in the wick. Heat pipes can transfer heat much more efficiently than conductive materials alone. They are used for electronics cooling, aerospace applications like satellites, and other applications requiring fast heat transfer over distance.