Experiments were performed to investigate the start-up and subsequent behavior of a water heat pipe with air-cooled fins for heat-source input steps from zero (frozen) to a constant level. First, the behavior of the water within the heat pipe was visualized, and measurements were made to obtain time-dependent wall-temperature profiles. It was found that the thermal resistance of the air-cooled fins is extremely small, the pipe causes dryout in the evaporator section, and wall temperature in that section rises rapidly. Second, measurements were made for different thermal resistance of the air cooled fins attached to the condenser section, different ambient temperatures, different heat inputs, and different charge rates of water. A correlation was obtained that can be used for successful start-up from the frozen state.
