Visualization and heat transfer comparative analysis of two phase closed thermosyphon

This study investigates the thermal performance and inner phase-change heat transfer behaviors of two phase closed thermosyphons with a corrugated evaporator (C-thermosyphon) by comparing them with a smooth thermosyphon (S-thermosyphon). Visualization and heat transfer experiments are conducted for the C-thermosyphons and S-thermosyphon under various heating conditions and filling ratios of the working fluid. The effect of corrugated pitch is also discussed. A comparison and analysis of the test results show that a corrugated evaporator offers better thermal performance and boiling stability for the thermosyphons. Geyser boiling is a common phenomenon in both types of thermosyphons at steady-state heat transfer. Visualization results suggest that the formation of a bullet-shaped bubble in the S-thermosyphon leads to an extremely high axial bubblegrowth rate and causes a severe liquid up-throwing phenomenon. However, for the C-thermosyphons, radial expansion of the bubble head is observed each time it reaches the annular groove of the corrugated pipe, which can considerably limit the axial bubble-growth rate while increasing the boiling disturbance. The results also show that the corrugated pipe at the evaporator of a thermosyphon can greatly stabilize the boiling heat transfer, thereby improving reliability.