Design Considerations
The three basic components of a heat pipe are:

    1. the container
    2. the working fluid
    3. the wick or capillary structure

Container
The function of the container is to isolate the working fluid from the outside environment. It has to therefore be leak-proof, maintain the pressure differential across its walls, and enable transfer of heat to take place from and into the working fluid.
Selection of the container material depends on many factors. These are as follows:

  • Compatibility (both with working fluid and external environment)


  • Strength to weight ratio


  • Thermal conductivity


  • Ease of fabrication, including welding, machineability and ductility


  • Porosity


  • Wetability

Most of the above are self-explanatory. A high strength to weight ratio is more important in spacecraft applications. The material should be non-porous to prevent the diffusion of vapor. A high thermal conductivity ensures minimum temperature drop between the heat source and the wick.