A device for transferring heat efficiently between two locations by using the evaporation and condensation of a fluid contained therein. Originally developed for refrigeration and spacecraft thermionic generator applications, heat pipes (and their close relative, the thermosiphon) have become routine components in systems ranging from missiles to domestic tuner-amplifiers and furnaces. They have many applications in areas where reliable performance and low cost are of prime importance—for example, in electronics and heat exchangers.