Operation principles and performance of heat pipes and closed two-phase thermosyphons

Heat pipes and closed two-phase thermosyphons are highly efficient heat transfer devices utilizing the continuous evaporation/condensation of a suitable working fluid for two-phase heat transport in a closed system. Due to a variety of advantageous features these devices have found a number of applications both in space and terrestrial technology. The operational principles and the performance characteristics of the different types of heat pipes are described. For the heat pipe designs which have found the widest application, viz. the classical capillary-wick heat pipes and the wickless heat pipes or closed two-phase thermosyphons, mathematical schemes are given to calculate the performance and performance limits.