Heat pipe

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A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.^[1]

At the hot interface of a heat pipe, a volatile liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. The vapor then travels along the heat pipe to the cold interface and condenses back into a liquid, releasing the latent heat. The liquid then returns to the hot interface through capillary action, centrifugal force, or gravity and the cycle repeats.

Due to the very high heat transfer coefficients for boiling and condensation, heat pipes are highly effective thermal conductors. The effective thermal conductivity varies with heat pipe length and can approach 100 kW/(m⋅K) for long heat pipes, in comparison with approximately 0.4 kW/(m⋅K) for copper.^[2]

Modern CPU heat pipes are typically made of copper and use water as the working fluid.^[3] They are common in many consumer electronics like desktops, laptops, tablets, and high-end smartphones.