Pulsating 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 pulsating heat pipe (PHP) [1][2] is made from a long capillary tube bent into many turns, with the evaporator and condenser sections located at these turns. There are two main types of PHPs--looped and unlooped (Fig. 1)—which are classified according to whether or not the two ends of the PHP connect.

Pulsating heat pipe (a) unlooped, (b) looped.
Figure 1: Pulsating heat pipe (a) unlooped, (b) looped.

A PHP is usually partially charged with a working fluid, with a charge ratio between 40% and 60%. Since the diameter of a PHP is very small (less than 5mm), vapor plugs and liquid slugs are formed as a result of capillary action. Heat input either causes evaporation or boiling, which increases the pressure of the vapor plug in the heating section. Simultaneously, the pressure in the cooling section decreases due to condensation. This pressure difference pushes the liquid slug and vapor plug into the cooling section. The liquid slug and vapor plug in the cooling section are then pushed into the next heating section, which will push the liquid slug and vapor plug back to the cooling section. This process enables the self-excited oscillatory motion of liquid slugs and vapor plugs. Heat is transported from the heating section to the cooling section via the pulsation of the working fluid in the axial direction of the tube. The unique feature of PHPs, compared to conventional heat pipes, is that there is no wick structure returning the condensate to the heating section. There is therefore no countercurrent flow between the liquid and vapor. The entrainment limit in the conventional heat pipe does not have any effect on the capacity of heat transport by a PHP. With this simple structure, the PHP weighs less than a conventional heat pipe, making it an ideal candidate for space applications. Since the diameter of the PHP is very small, surface tension plays a greater role in the dynamics of the PHP than gravitational force does, enabling successful operation in a microgravity environment. Other applications of PHPs include thermal control of electrical and electronic devices and components, as well as thyristors, diodes and ceramic resistors. Zhang and Faghri [3] made a comprehensive review related to existing experimental and theoretical research in pulsating heat pipes.


  1. Faghri, A., 2012, "Review and Advances in Heat Pipe Science and Technology," Journal of Heat Transfer, 134(12), 123001. http://dx.doi.org/10.1115/1.4007407
  2. Faghri, A., 1995, Heat Pipe Science and Technology, 1st ed., Taylor & Francis, Washington, D.C.
  3. Zhang, Y., and Faghri, A., 2008, "Advances and Unsolved Issues in Pulsating Heat Pipes," Heat Transfer Engineering, 29(1), 20-44. http://dx.doi.org/10.1080/01457630701677114