Capillary-Driven Heat Pipe

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Types of Heat Pipes
  1. Two-Phase Closed Thermosyphon
  1. Capillary-Driven Heat Pipe
  1. Annular Heat Pipe
  1. Vapor Chamber
  1. Rotating Heat Pipe
  1. Gas-Loaded Heat Pipe
  1. Loop Heat Pipe
  1. Capillary Pumped Loop Heat Pipe
  1. Pulsating Heat Pipe
  1. Monogroove Heat Pipe
  1. Micro and Miniature Heat Pipes
  1. Inverted Meniscus Heat Pipe
  1. Nonconventional Heat Pipes

The capillary-driven heat pipe (conventional heat pipes) consists of a sealed container, in which a wick is placed on the inner radius of the pipe wall (Fig. 1) [1][2].

Conventional capillary-driven heat pipe.
Figure 1: Conventional capillary-driven heat pipe.

The purpose of the wick is to provide a capillary-driven pump for returning the condensate to the evaporator section. Enough working fluid is placed inside the sealed pipe to saturate the wick with liquid. The operation of the capillary-driven heat pipe is as follows. Heat input to the evaporator section evaporates the liquid in the wick. The vapor then enters the vapor space and travels to the condenser section due to the higher vapor pressure in the evaporator. Heat removal from the condenser causes the vapor to condense, releasing its latent heat of vaporization. The condensate is then pumped back to the evaporator section by the capillary force generated at the liquid-vapor interfaces of the pores in the wick. Due to the two-phase nature of the capillary heat pipe, it is ideal for transferring heat over long distances with a very small temperature drop, and for creating a nearly isothermal surface for temperature stabilization. Generally, the most commonly encountered limitation to the performance of a capillary-driven heat pipe is the capillary limit. This occurs when the wick cannot return enough liquid to the evaporator section to keep it saturated. At this point, the evaporator wall experiences a sudden, continuous increase in temperature. Conventional capillary heat pipes are used in almost all laptop/notebook computers nowadays to channel heat away from the processors. The capillary heat pipe has also been widely applied to various commercial and aerospace applications.


  1. Faghri, A., 2012, "Review and Advances in Heat Pipe Science and Technology," Journal of Heat Transfer, 134(12), 123001.
  2. Faghri, A., 1995, Heat Pipe Science and Technology, 1st ed., Taylor & Francis, Washington, D.C.