The heat pipe functioning

Among classical cooling systems, the heat pipe functioning hold a particular position because of it is a passive solution. Patented in 1942, the heat pipe technology has been widely used during the sixties for space applications. It is now more and more used for industrial applications.

Thermal management for electronic components is a main issue in the performance of power converters and computers. Performance of electronics components is currently improving, leading to huge amount and high density of power.

How it works ?

A heat pipe is made by a sealed enclosure, a working fluid and a capillary network. During the manufacturing process, all the air enclosed in the pipe is removed. We insert the suitable quantity of fluid in order to fill up the capillary network. A balance between liquid phase and vapor phase is created.

When the heat is applied to one of the end of the pipe (evaporator area), the working fluid is transforming into vapor. This leads to a light increase of pressure that moves the vapor to the other end of the pipe (condenser area). In the condenser area, vapor is transforming back into liquid. The liquid is flowing through the capillary networks and then come back to the evaporator side with the help of gravity (thermosiphon) or the capillary pumping effect (heat pipe). The cycle can be renewed indefinitely, it is autonomous and without any maintenance.

During the evaporation of the liquid the fluid absorbs energy. In return, it gives back energy during condensation of the vapor. Thus there is an overall thermal transfer between evaporator and condenser with a very small difference of temperature. The middle area between evaporator and condenser is adiabatic. This area can reach few meters, that allows heat transfer over high distances.

If you compare a heat pipe, with a full copper bar having the same dimensions, subjected to the same difference of temperature, the heat pipe has about 1000 time more thermal conductivity.

Position and size of the hot/cold sources can be variable. It is also possible to have several hot/cold sources. However accurate characteristics, are depending from the positions of these sources and pipe diameter.

The heat pipe is only a way to convey heat. If it is requested to dissipate the power to the air, it is necessary to set fins in order to increase exchange surface. A base plate is generally set up on evaporator in order to collect calories from the hot source (electronic components). As usual for thermal management, all the interfaces have to be flat and continuous for a good overall performance.


Working fluid

Enclosure/Fluid classicaly used, and temperature ranges:

  • Copper / Water: [+5°C ;+250°C] – Standard solution for electronic
  • Copper / Ethanol: [-45°C ;+130°C] – Cold start applications
  • Aluminum / Ammonia: [-60°C ; +70°C]
  • Stainless steel / Ammonia: [-60°C ; +70°C]


  • Gravity heat pipe or Thermosiphon: pipe working with the help of gravity. It is requested that the hot source is below the cold source, with a minimum angle of 3° / horizontal
  • Heat pipe with capillary structure: pipe working with capillary pumping. The negative inclination compared to horizontal can be allowed (hot source higher than cold one)


  • From 5W to 1000W per pipe
  • Pipes can be added in parallel to achieve higher thermal transfer

Thermal resistance and delta T°

  • Depending from functioning point


  • Diameter: 3mm to 16mm
  • Length : 50mm to 5000mm


Type of cooler we can provide

  • Surface / Air or Air / Surface
  • Surface / Surface
  • Air / Air
  • Spreader

Capillary pumped loop (CPL)

Capillary pumped loop, have been derivated from heat pipe principle. Liquide phase is separated from vapor in the same closed loop.

CPLs are built with an evaporator area, a capillary structure and a condenser area. Heat flux on the evaporator is leading to a pressure increase in the capillary structure. The pressure increase push the working fluid to flow in the loop.

CPLs are interesting because of their resistance against high accelerations. Most of CPLs are used for spatial applications.

They are however hard to set up, because of the transitory cycles that may happen during start and stop.

The heat pipe functioning

The technology

Selenium rectifiers and suppressors are still used in the industry for their strong reliablity. This technology has been mainly replaced by silicon diodes, providing a better efficiency and lower voltage drop. Selenium components are very interesting for their reliability. Those components have the ability to recover after surge failure, which make them excellent for security applications. COUGAR ELECTRONICS has been one of the leading company in the 50's. We are the last firm still manufacturing parts made in USA thanks to our CT factory.

Elevator industry, Military and power generation

Despite most of our business is now focused on up to date semionductors like silicon diode, thysirtors, IGBT and SiC, our manufacturing department is serving elevator industry (otis, schindler, kone, thyssen krupp). We also serve specific fields like military or power generation application .

Service and Fast delivery

Our excellence in organisation, allow us to serve after-sales service with exceptional fast deliveries :
  • same day shipping
  • next day shipping

Looking for a part, call us !

If you look for a specific part number, or even if you do not have part number. Do not hesitate to call us. We build and design any type of selenium rectifier or selenium suppressor. Do not give up, thinking these components are impossible to find. We are here to help ! [caption id="attachment_2376" align="alignnone" width="282"]selenium rectifier selenium rectifier[/caption] [caption id="attachment_2370" align="alignnone" width="297"]Selenium7 Rectifier 3 phases[/caption] [caption id="attachment_2369" align="alignnone" width="210"]Selenium Suppressor Surge Suppressor[/caption]

Troubleshooting a selenium rectifier or suppressor

Our customer service will be happy to help you to determine what's the best solution.

Find parameters for rectifiers :

  • Voltages: Standard Voltages per cell up to 36 v rms. The voltage rating is determined by the number of cells in series
  • Current: Ratings are determined by the size of the cell or the number of cells in parallel. The circuit configuration and the type of cooling are also important factor to consider.
  • Circuits: Half wave, Doublers, Center Taps, Full Wave Bridges, single and three phase.

Find parameters for suppressors :

  • Ratings: Determined by the cell size and number of cells in a series (similar to rectifiers above).
  • Suppressors are also rated by the voltage clamping factor and the amount of reverse energy they can absorb (in joules).

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