Heat Pipe Resources

Heat Pipe assemblyAdvanced Cooling Technologies, Inc. is the trusted expert in heat pipe products and technologies. ACT manufactures a large variety of heat pipes, heat pipe heat sinks, and heat pipe assemblies for a wide range of applications in a variety of markets. In fact, ACT is the only US manufacturer that routinely delivers heat pipes for terrestrial electronics cooling (copper-water), on-orbit satellite thermal management (aluminum-ammonia and copper-water) and high-temperature calibration equipment (liquid metal). In addition, ACT is the partner of choice in developing new functionality and increased performance with emerging heat pipe technology.

This Heat Pipe Resource page contains the most extensive information on heat pipes and related technology available anywhere on the web, including Fundamentals, Limits, Wicks, Working Fluids and Envelopes, Different Kinds of Heat Pipes, and Advanced Developments.

An Overview of Heat Pipe Technology

A heat pipe is a two-phase heat transfer device with a very high effective thermal conductivity.  It is a vacuum-tight device consisting of an envelope, a working fluid, and a wick structure.  As shown in the video below, the heat input vaporizes the liquid working fluid inside the wick in the evaporator section. The saturated vapor, carrying the latent heat of vaporization, flows towards the colder condenser section.  In the condenser, the vapor condenses and gives up its latent heat.  The condensed liquid returns to the evaporator through the wick structure by capillary action.  The phase change processes and two-phase flow circulation continue as long as the temperature gradient between the evaporator and condenser are maintained.

Benefits of Using Heat Pipes:

  • High Thermal Conductivity (10,000 to 100,000 W/m K)
  • Isothermal
  • Passive
  • Low Cost
  • Shock/Vibration tolerant
  • Freeze/thaw tolerant

Please click on the icons below to learn more about heat pipes.

If you are designing a thermal system and simply want to learn more about heat pipes for cooling, use the links in the Operation Section. If you still have questions, contact us and an engineer will be in contact with you.

Read more about heat pipes in our Heat Pipe FAQ, or download our Heat Pipe Reliability Guide.  See a full video and transcription about the basics of heat pipes and their advantages.

Resource Pages

How do they work?

Background physics including a video that demonstrates the two-phase heat transport.

Heat Pipe FAQ

Frequently asked questions about basic heat pipe fundamentals.

Heat Pipe Reliability Guide

This printable, easy-to-follow guide will provide you with the following information for copper/water heat pipes: A step-by-step guide for designing heat pipes into your system, Modeling, Practical Reliability


Learn about the various limits that determine the maximum power (W) a heat pipe can move.


Use this tool to calculate a copper-water heat pipe's capability for your system.

Design Guide

Learn the basics on sizing and modeling with our heat pipe design guide. You'll be able to integrate these devices into your project in no time!

More pictures

Visit galleries of two-phase heat transfer devices.

Wick Structures

Learn about the advantages, limitations, and trade-offs of various wick structures.

Fluid Selection / Compatibility

Working fluids are determined primarily by the ambient conditions, the thermodynamic properties of the fluid, and compatibility with the wick/envelope.

Different Types of Heat Pipes

Discusses specialized heat pipes and their applications.


Video with a transcript that discusses fundamental operating principles of heat pipes.


Learn how to integrate heat pipes into computer models.


A short history showing how applications have expanded since the heat pipe was invented back in 1963.


ACT’s thermal management video tutorials, including two-phase heat transfer, heat sinks, LED thermal management, and thermal storage. Transcriptions of the videos are available.

Related Brochures

Our brochures provide an overview of various product categories.

New Advancements

Advanced Heat Pipes and Loop Heat Pipes

Advanced Heat Pipes and Loop Heat Pipes including new working fluids, passive thermal control with variable conditions, and freeze/thaw tolerance.

High Temperature Water Heat Pipes

Learn how ACT has extended the operating temperature range for water working fluid from 150 to 300°C.

Intermediate Temperature Working Fluids

ACT is developing new working fluids for the intermediate temperature range, between water and alkali metal working fluids.

High Temperature

Alkali metal working fluids with superalloy envelopes allow operation at temperatures up to 1100°C.

Vapor Chambers

ACT has developed vapor chamber heat spreaders that can accept heat fluxes up to 500 W/cm2 over a 4 cm2 area and transform the heat flux so that it can be removed with conventional cooling methods.

Pressure Controlled Heat Pipes (PCHPs)

PCHPs vary the amount of Non Condensable Gas (NCG) in their reservoir, allowing very tight temperature control (± 5 mK) over hours of operation.

Loop Heat Pipes

LHPs are passive, two-phase heat transport devices that can transfer higher amounts of heat over longer distances than conventional heat pipes.

High Temperature Water Heat Pipe Radiators

High temperature titanium-water heat pipes with radiators have been developed for use in spacecraft fission power systems.

Heat Pipe Loops (HPLs)

HPLs provide higher heat transport than heat pipes, with lower cost than LHPs.

Life Tests

Life tests are conducted to verify that the envelope, wick, and working fluid in a two-phase heat transfer device are compatible, allowing for long term operation.

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