Heat pipes are self-contained heat pumps that can transport heat at high rates over fairly substantial distances with no external pumping power. Heat pipes are made out of aluminum or copper and are lined with a wicking material such as a ceramic or carbon fiber that provides capillary action. A liquid inside the heat pipe is heated and enters the porous wicking material, saturating the inside of the heat pipe. The gas that results from the heated liquid moves heat from the input end of the heat pipe to the output end. Heat pipes are typically constructed with an evaporator section, where the liquid is heated, and a condenser section where the gas cools and condenses.

Heat piping is used in applications ranging from cryogenics and aerospace to home appliances such as air conditioners and refrigerators. Heat pipe technology is also used in circuit boards or computers. A flat heat pipe or thin heat pipe is used in conjunction with airflow from fans to regulate the computer’s temperature. The selection of a copper heat pipe is common for many applications.

Other types of heat pipes include heat exchangers. A heat exchanger is a device used in mostly industrial applications for transferring heat between two different liquids. A double pipe heat exchanger consists of two heat pipes, one inside the other and is also known as a recuperator, or closed-type exchanger. In an open-type exchanger, the two liquids are allowed to mix with each other and exit the heat exchanger in one stream. In a double pipe heat exchanger, the hot and cold liquids do not contact each other. The heat energy instead flows from one liquid to the outer surface of one pipe using forced convection, then through the wall of the pipe by conduction and from the inside surface of the pipe to the second fluid by forced convection.