2. Thermosyphon heat pipe

This is a natural fluid circulation heat pipe which has no wick material presence. It is a simple heat pipe consisting of a sealed vessel charged with working fluid under a vacuum condition. It is made up of evaporator and condenser sections, sometimes with adiabatic section in between them. The vessel is usually made from aluminium or copper to facilitate high conduction of heat. Unlike wick heat pipe, the condenser of thermosyphon must be at the top, for the condensed liquid to return to the evaporator under gravity. Furthermore, some applications of thermosyphon require that the pipe be tilted to an angle from the horizontal for it to have maximum exposure to solar radiation [9, 14–16].
