Performing three-dimensional numerical analysis of a thermosyphon heat pipe performing thermal energy transfer from liquid to gas

Most of the numerical analysis studies carried out to model the evaporation-condensation processes of Two-Phase-Closed thermosyphons (TPCT) have been carried out in 2D. However, performing Computational Fluid Dynamics (CFD) analyzes in 3D will provide a better understanding of the heat and mass transfer processes together with the complex flow events that occur in TPCTs with finned structures. In this study, the experimental and comprehensive 3D CFD analyzes were carried out to model in detail the evaporation-condensation and heat transfer process of TPCTs with 25mm and 40mm outer diameters, which have a from-end-to-end finned structure. CFD analyzes were performed using ANSYS Fluent software. The Volume of Fluid (VOF) method was used to monitor the liquid-vapor interface motion. R404A refrigerant is designated as working fluid. In order to model the evaporation-condensation phenomenon, the terms mass and energy source were added to the governing equations in the Fluent program with a User Defined Functions (UDF) prepared in the C programming language. The average temperature results obtained from CFD and experimental analyzes were compared and it was seen that they were in good agreement. Evaporation and condensation and the heat transfer process have been successfully modeled and visualized. The time-delayed condensation event that occurred in the condenser section, which has become a problem especially in the literature, was prevented by the selected mass transfer time relaxation parameters in accordance with the experimental results, and condensation occurred without time delay with the start-up of the TPCT in the aforementioned study.