Condensation heat transfer characteristics and concept of sub-flooding limit in a two-phase closed thermosyphon

A condensation model is developed for a two-phase closed thermosyphon by considering the interfacial shear due to mass transfer and interfacial velocity. The model predictions differ substantially from Nusseltʹs solutions, showing the significance of the interfacial shear on the condensation inside the thermosyphon. It is found that the condensation heat transfer is greatly affected by two controlling parameters—the relative velocity ratio B and the momentum transfer factor U. The sub-flooding limit, which is different from the conventional flooding limit, is proposed to capture the interaction between the condensation and evaporation in the thermosyphon, based on which the critical aspect ratio (radius/length) can be determined to prevent the thermosyphon from heat transfer deterioration.