Advanced Heat Pipes and Loop Heat Pipes

Since its beginning in the early 1960s, the heat pipe technology has evolved into many different shapes and forms and has been used in numerous applications from computer cooling to spacecraft thermal control. Our Heat Pipe Resources page has the most extensive information on the web about heat pipe operation and limitations.

Standard heat pipes act as thermal superconductors, transmitting heat with minimal temperature drop in both directions.  By adding small amounts of Non-Condensable Gas (NCG) and modifying the heat pipe design, it is possible to create many heat pipe variations, such as the following:

  • Diode Heat Pipes, which transfer heat in one direction, and shut down when heat is supplied to the nominal condenser
  • Variable Conductance Heat Pipes (VCHPs), that can maintain the evaporator temperature during wide swings in the power, and in the heat sink conditions,
  • Pressure Controlled Heat Pipes (PCHPs), which can provide precise temperature control.  They can also be used to switch the heat flow path at high temperatures, using low-temperature components
  • Heat Pipe Switches, that passively turn on and off to maintain a component above a set-point temperature

Other advanced heat pipes include high heat flux vapor chambers (> 1,000 W/cm2), as well as heat pipes with new working fluids and envelopes for the temperature range between 150 and 450°C.

Loop Heat Pipes (LHPs) have been developed with a Thermal Control Valve (TCV), allowing the LHP to passively shut down to maintain the evaporator temperature during the 14 day long Lunar night. Heat Pipe Loops offer higher power than heat pipes, while are lower cost than LHPs. Watch this video presentation made for ICES 2021 to learn more!

The following pages contain information on our experience with various advanced forms of heat pipes:

High-Temperature Water Heat Pipes 150 to 300°C

High-Temperature Monel and Titanium Heat Pipes have been developed that extend the temperature range for water from 150 to 300°C

Intermediate Temperature Heat Pipes

Intermediate Temperature Heat Pipes have been developed that operate from 450 to 750 K, between water and alkali metal working fluids

High-Temperature Heat Pipes

High-Temperature Heat Pipes use alkali metal working fluids with superalloy envelopes up to 1100°C, and refractory metal envelopes at higher temperatures

Vapor Chambers

ACT’s Vapor Chambers can use direct-bond copper for mounting electronics, and accommodate heat fluxes up to 1000 W/cm2

Variable Conductance Heat Pipes

Variable Conductance Heat Pipes (VCHPs) have a non-condensable gas loading to help maintain the evaporator temperature under changing conditions

Pressure Controlled Heat Pipes

Pressure Controlled Heat Pipes are a type of VCHP that allows the temperature to be controlled as tightly as ± 5 milli-Kelvin

Hybrid CCHPs: axial grooved adiabatic and condenser sections - screen mesh or sintered evaporator wick.

Hybrid Wick Heat Pipes for Operation in Microgravity and on Planetary Surfaces

Hybrid wicks with a screen/sintered evaporator wick allow grooved heat pipes to operate on planetary surfaces, such as the Moon and Mars.

Loop Heat Pipes

Loop Heat Pipes (LHPs) are passive, two-phase heat transfer devices that can carry more power and operate at higher adverse elevations than heat pipes

Heat Pipe Loops

Heat Pipe Loops, invented at ACT, offer higher performance than heat pipes with much lower costs than Loop Heat Pipes

Heat Pipe Life Tests

Heat Pipe Life Tests are necessary to determine compatibility between the envelope, wick, and the working fluid

High Heat Flux CCHPs

Using a hybrid wick can increase the allowable evaporator heat flux in Constant Conductance Heat Pipes (CCHPs) by more than a factor of three.

High-Temperature Water Heat Pipe Radiators

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


High-Heat-Flux (>50 W/CM2) Hybrid Constant Conductance Heat Pipes

ACT’s high heat flux CCHPs will eliminate the need of using these heat spreaders and will address a need of more demanding spacecraft thermal performance.

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