Two-phase thermal links use the circulation of liquid and vapor at thermal equilibrium. They are capable of transferring high thermal power over several meters. The capillary forces, the gravity forces or oscillations generated by evaporation and condensation processes are used for the fluid circulation. The fluid (hydrocarbon, nitrogen, helium) is chosen according to the working temperature. At cryogenic temperatures, these thermal links must be primed or pre-cooled before operation. The priming system designed by SBT features two reservoirs with liquid and vapor at saturation and thermally anchored to the cold source. They are connected together with a capillary tube via the object to be cooled. One reservoir is heated, the pressure increases and pushes the liquid outside of it towards the object to be cooled where it evaporates. Then the vapor is condensed in the other reservoir. The alternate heating of the two reservoirs quickly drains heat from the object towards the cold source.

This priming system has been successfully used and tested for the pre-cooling of a cryogenic pulsating heat pipe.