Modeling and performance analysis of a two-phase thermosyphon loop with partially/fully liquid-filled downcomer

• Model for thermosyphon loop with partially/fully liquid-filled downcomer is developed.
• Internal parameter distribution along the loop is presented.
• Less refrigerant charge more likely results in partially liquid-filled downcomer.
• Downcomer is partially liquid filled in the case of small temperature difference.

Two-phase thermosyphon loops (TPTLs) are extensively used in industries. Numerical simulation is always applied for their configuration design and performance rating. The conventional models are usually developed under large temperature difference, and the fully liquid-filled downcomer are taken for granted. In this study, a generalized model for TPTL is developed, in which the downcomer can be partially liquid filled or fully liquid filled under different conditions. The model is verified by experiments on an air-to-air finned-tube TPTL. Then, it is used to analyze the flow and heat transfer features of a TPTL, under different refrigerant charge and temperature difference. The results show that the downcomer is partially liquid filled in the case of small temperature difference and refrigerant charge. Additionally, the heat transfer rate first increases then decreases with the increase of refrigerant charge, and first increases linearly then increases relatively slowly with the increase of temperature difference.