Heat pipes and Thermosyphons

Heat is transferred as latent heat of evaporation which means that the fluid inside the system is continuously changing phase from liquid to gas.
• The fluid is evaporating at the hot end, thereby absorbing heat from the component.
• At the cold end, the fluid is condensed and the heat is dissipated to a heat sink(usually ambient air).

Heat pipes
• In Heat Pipes, capillary forces in the wick ensures the liquid return from the hot end to the cold end.
• This means that a Heat Pipe can operate independent of gravity. The heat pipe was actually developed for zero gravity (i.e.space) applications.