Vapor chamber heat pipes use evaporation and condensation to help transfer heat through the material. Heat evaporates the fluid, causing the vapor to rise to the top of the heat pipe. At the top, the heat transfers out of the heat pipe, cooling the fluid so it condenses and falls back to the bottom of the heat pipe.
I used a heat pipe in the portable refrigerator for my Senior Capstone project. The heat sink at the bottom of the heat pipe helps absorb heat from the box, and the heat travels up the heat pipe. At the top, a thermoelectric module creates a temperature difference and transfers the heat to the heat sink.