Numerical investigations on the thermal performance of two-phase closed thermosyphon with extended condenser surface

A comprehensively two-dimensional model is established to investigate the thermal performance of two-phase closed thermosyphon (TPCT) charged with acetone. A Volume of Fluid (VOF) method is utilized to simulate the phase change and two-phase flow behaviors. The mass and heat transfer process during the evaporation and condensation are implemented by a user-defined function (UDF) source. The application of thermosyphon can meet the requirements of space structure of battery pack and transfer massive heat from the cell to the environment by phase change mechanism. Additionally, an extended condenser surface of the thermosyphon is developed to enhance the heat transfer performance of liquid film condensation by extended surface, which is estimated by several indicators in terms of temperature distribution, vapor volume fraction, thermal resistance, wall heat transfer coefficient, and velocity. The results reveal that TPCT with extended condenser surface can maintain a great thermal homogeneity and generate well-distributed bubbles along the vertical axial without heat accumulation at the upper zone of evaporator section. Compared with normal condenser, the total thermal resistances decrease by 5%, 25.7% and 17.0% respectively, while the heating power are 5 W, 10 W and 15 W. Moreover, higher power inputs can significantly accelerate the formation of bubbles at the boiling pool, as well as the droplets and liquid film at the condenser section, which increase the thermal performance of thermosyphon.