Heat Pipes

A Heat pipe is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces.

A heat pipe can be described as a closed, evacuated tube lined with a porous structure on the inside walls. This porous structure is called “wick structure”, and it is saturated with an appropriate amount of working fluid (typically water – for use in normal temperatures). When a portion of the heat pipe is exposed to heat:

  • The fluid in the heated portion vaporizes (picking up thermal energy – latent heat of vaporization)
  • The vapor flows to the cooler portion of the container
  • The vapor cools and condenses (releasing thermal energy – latent heat of condensation)
  • Condensed fluid is returned by capillary action to the hotter portion of the heat pipe.

This thermodynamic cycle continues as the thermal energy is transferred from one end to the other. In a heat pipe under heat load, the temperature will remain constant as the working fluid goes through the phase change inside the heat pipe chamber, hence making the heat pipe a very efficient heat transfer device.

Heat pipes are totally passive heat transfer systems. This means they have no moving parts to wear out, and require no electrical energy to operate. They offer the design engineer low cost packaging and flexibility because they can be manufactured in a variety of different shapes and sizes as per the requirement and preferences of the customer / end user. Their light weight and compact size also make them the ideal choice for space-constrained applications. 

At the hot interface within a heat pipe, which is typically at a very low pressure, a liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. The vapor condenses back into a liquid at the cold interface, releasing the latent heat. The liquid then returns to the hot interface through capillary action where it evaporates once more and the cycle is repeated.”

Advantages of Heat pipe

  • High thermal conductance – higher wattage removed. Capability to control thermal flux.
  • 20 to 40% reduction in weight and volume compared to thermal solution not using heat pipe.
  • Very long life (>10-20 years)
  • Cost comparable to conventional extruded heat sinks.
  • No maintenance – No moving parts.
  • No restriction on orientation of heat sink.