What is a Heat Pipe?
A heat pipe is a type of heat exchanger that uses the evaporation and condensation of a liquid to transfer heat. The use of phase changes make heat pipes significantly more effective as heat transfer devices than ones that utilize conduction through a material alone. Heat pipes are closed systems that can function completely on their own without any power input [1].
Typical designs are composed of copper or aluminum pipes sealed shut on both ends. (Cu and Al are used due to their high thermal conductivities) On the inside, there is a fluid–usually water but sometimes other compounds such as liquid ammonia or propylene glycol will be used too. When one end of the pipe is heated, the heat is transferred to the liquid, mostly in the form of latent heat. The liquid then evaporates and drifts toward the other, cooler end of the pipe via convection. The lower temperature of the other end causes the liquid to then condense, thereby releasing the latent heat into the cooler end of the pipe. This heat can then either be either used to heat something else or can be dispersed into the surrounding atmosphere through a heat sink.
The liquid is then moved back toward the hot end of the pipe. This can be done via gravity or capillary action. Heat pipes most commonly use the latter by adding in a wick along the inner wall of the pipe. Upon return of the condensate to the hot end of the pipe, the cycle starts again providing continuous heat transfer. The complete cycle of heat transfer is shown in Figure 1.
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| Figure 2: Animated diagram of heat pipe function |
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