Axially Grooved Thermal Siphon uses a circle of grooves in the interior wall of the heat pipe envelope as the wick efficiently pulls condensate back to the evaporator from the cooler surfaces where working fluid had condensed. The Siphon is ideal for satellite thermal management applications. The Siphon is used in applications with radial heat fluxes up to 40 W/ cm2. The Axially Grooved Thermal Siphon ensures a variety of options for cooling electronic components in various challenging locations.