A heat pipe or heat pin is a heat-transfer device that combines the principles of both thermal conductivity

Thermal conductivity

In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

 and phase transition

Phase transition

A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another.A phase of a thermodynamic system and the states of matter have uniform physical properties....

 to efficiently manage the transfer of heat between two solid interfaces

Interface (chemistry)

An interface is a surface forming a common boundary among two different phases, such as an insoluble solid and a liquid, two immiscible liquids or a liquid and an insoluble gas. The importance of the interface depends on which type of system is being treated: the bigger the quotient area/volume,...

.

At the hot interface within a heat pipe, which is typically at a very low pressure, a liquid

Liquid

Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 in contact with a thermally conductive solid surface turns into a vapor

Vapor

A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....

 by absorbing heat from that surface. The vapor condenses back into a liquid at the cold interface, releasing the latent heat.