On the performance limit of closed two-phase thermosiphons

This paper discusses an experiment conducted to investigate the performance limit of closed two-phase thermosiphons, together with visual observations of the flow state in the adiabatic section. The working fluids were R-113, methanol, and water. The flow state at the performance limit conditions was a violently disturbed slug type, in which the vapor plugs held up the liquid slugs periodically to a high level, causing a local circulation of liquid in the adiabatic section. This phenomenon is somewhat different from the flooding observed in open systems. An equation correlating the vapor velocity at the performance limit to the rising velocity of vapor plugs in stagnant liquid columns is proposed. This correlation compares satisfactorily with the performance limit data covering a wide range of parameters