heatpipes

Heat pipes are sealed, vacuum-filled devices that transfer heat efficiently by exploiting the latent heat of a working fluid. They typically consist of an evaporator section where heat is absorbed, a condenser section where heat is rejected, an adiabatic section linking the two, and a wick or other capillary structure that returns liquid to the evaporator.

Operation relies on phase change. When heat is applied at the evaporator, the working fluid vaporizes and the vapor travels to the cooler condenser, releasing latent heat and condensing. The liquid then returns to the evaporator through the wick by capillary action, gravity, or other return mechanisms in loop configurations. The cycle repeats with minimal moving parts, enabling continuous heat transport with a relatively small temperature difference between hot and cold regions.

Performance is characterized by very high effective thermal conductivity and a passive operation that requires no external power. Factors affecting performance include the heat input, ambient conditions, orientation (for some designs), wick structure and pore size, and the properties of the chosen fluid. The maximum transport capability is limited by the capillary return (the capillary limit), potential dry-out of the evaporator, and thermal resistance within the evaporator and condenser regions. Temperature range and chemical compatibility between the fluid and container materials are also important.

Variants and applications include loop heat pipes, pulsating heat pipes, and vapor chambers. Common terrestrial uses are electronics cooling, laptop and computer heat management, and spacecraft thermal control, while other applications include solar thermal receivers and high-performance power electronics cooling.