The open type of heat pipe is an interesting form of heat pipe. If the same fluid is used as the heat sink for the condenser as for the working fluid, non-condensing gas in the heat pipe, such as is evolved in a carbon steel-water heat pipe, can escape through a porous plug in the top.
The paper deals with the analysis of heat transfer in an open heat pipe and discusses the experimental results from such a heat pipe with water as the working fluid. The behaviour of the heat pipe was studied by monitoring the temperature in the condenser section of the heat pipe, both during the unstable conditions at start up and with different input powers.
Visual observations of the liquid inside a glass open heat pipe shows the two-phase flow in the pipe is similar to that in a closed thermosyphon, once water filling the heat pipe is expelled through the porous plug at the top.