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Efective thermal conductivities (5,000 Watts/meter·K to 200,000 Watts/meter·K), energy-efficiency, light weight, low cost and the flexibility of many different size and shape options. As passive heat transfer systems, heat pipes offer simple and reliable operation, with high effective thermal conductivity, no moving parts, ability to transport heat over long distances and quiet vibration-free operation. Heat pipes transfer heat more efficiently and evenly than solid conductors such as aluminum or copper because of their lower total thermal resistance. The heat pipe is filled with a small quantity of working fluid (water, acetone, nitrogen, methanol, ammonia or sodium). Heat is absorbed by vaporizing the working fluid. The vapor transports heat to the condenser region where the condensed vapor releases heat to a cooling medium. The condensed working fluid is returned to the evaporator by gravity, or by the heat pipe's wick structure, creating capillary action. Both cylindrical and planar heat pipe variants have an inner surface lined with a capillary wicking material.
What is a Heat Pipe?
Heat pipes are the most common passive, capillary-driven of the two-phase systems.Two-phase heat transfer involves the liquid-vapor phase change (boiling/evaporation and condensation) of a working fluid. The heat pipe technology industry leader, Thermacore has specialized in the design, developmentand manufacturing of passive, two-phase heat transfer devices since 1970.
Heat pipes have an extremely effective high thermal conductivity. While solid conductors such as aluminum, copper, graphite and diamond have thermal conductivities ranging from 250 W/m•K to 1,500 W/m•K, heat pipes have effective thermal conductivities that range from 5,000 W/m•K to 200,000 W/m•K. Heat pipes transfer heat from the heat source (evaporator) to the heat sink (condenser) over relatively long distances through the latent heat of vaporization of a working fluid. Heat pipes typically have 3 sections: an evaporator section (heat input/source), adiabatic (or transport) section and a condenser section (heat output/sink).
Key Components of a Heat Pipe
The three major components of a heat pipe include:
- A vacuum tight, sealed containment shell or vessel
- Working fluid
- Capillary wick structure
They all work together to transfer heat more efficiently and evenly. The wick structure lines the inner surface of the heat pipe shell and is saturated with the working fluid. The wick provides the structure to develop the capillary action for the liquid returning from the condenser (heat output/sink) to the evaporator (heat input/source). Since the heat pipe contains a vacuum, the working fluid will boil and take up latent heat at well below its boiling point at atmospheric pressure. Water, for instance, will boil at just above 273° K (0°C) and start to effectively transfer latent heat at this low temperature.