Thermosyphons are devices, which use the property of boiling fluids to remove high heat fluxes under relatively low temperature differences and high heat transfer coefficients. These devices have found wide application in the development of satellites, electrical and combustions motors, air conditioning systems, power plants, etc. The wide use of thermosyphons for cooling of electronic components makes it possible to develop devices with small dimensions and high power.
The present work is a necessary step in the development of a new thermosyphon cooling system for large electrical machines. It is concentrated on the investigations of the boiling processes in mini-channel thermosyphons. Specially developed test sections with 40cm mini-channel, 1m mini-channel and parallel 1m mini-channels thermosyphons are constructed in order to observe the flow in the channels and to measure the respective heat transfer coefficients. The measurements show that the heat transfer coefficients of all channels have comparable values. The flow patterns in the channels were mostly stratified or stratified-wavy. It was proven that the channel orientation does not play a significant role in the heat transfer. The influence of the filling amount of fluid on the boiling processes was systematically investigated and it was found that it affects considerably the boiling process in thermosyphons.