Abstract: A heat pipe has its evaporator at its upper end and its condenser at its lower end and an adiabatic section separating the two so that capillary wicks or grooves do not extend through the heat pipe. A central liquid return tube extends between the evaporator and condenser. A vapor bubble generator is placed at the condenser section in the reservoir where the liquid state of the working fluid collects. When the vapor bubble generator is operated, bubbles form which, because of their buoyancy, will rise to the top of the central tube. As they rise, small amounts of working fluid in its liquid state will be carried with the bubbles and spill over the top of the tube and onto the evaporator wick. As a consequence, the heat pipe is insensitive to its vertical height and can operate against gravitational forces.