Heat pipe is a device that transfers large amounts of heat from one place to another with only small amounts of heat loss. Heat pipes can transport much more heat per unit area than the best metal conductors, including copper and silver. Unlike most heat transfer devices, they require no external power source. This feature makes them more energy-efficient and more economical.
Heat pipes are used to remove waste heat from certain types of electronic equipment and industrial machinery. In many cases, they carry this heat to another place where it can be used. Some air-conditioning and heating systems employ heat pipes to regulate temperature. Heat pipes also have been used for such purposes as controlling the temperature in spacecraft and transporting heat from solar energy collectors.
A heat pipe consists of a metal tube that is sealed at both ends and lined with a porous material. The lining, called the wick, holds a liquid, such as water, methanol, or molten lithium. This liquid is known as the working fluid. It absorbs heat from a heat source at one end of the tube and vaporizes. The vapor flows out of the wick and builds up pressure at the hot end of the tube. This pressure causes some of the vapor to travel to the cooler end of the tube. There the vapor condenses as it cools, transferring its heat through the tube wall. The liquid returns to the warmer end of the tube through the wick as a result of capillary action (see Capillary action ).
The temperature of the heat delivered by a heat pipe is roughly equal to the working fluid’s boiling point, the temperature at which the liquid bubbles and vaporizes. The boiling point remains constant as long as the atmospheric pressure does not change, so a heat pipe provides precise temperature control.
