Performance enhancement of a two-phase closed thermosyphon with a vortex generator

Abstract

This study focuses on improving the heat transfer performance of a two-phase closed thermosyphon by altering the geometry of a typical straight pipe thermosyphon body. Here, a vortex generating obstacle positioned in the pipe body augments the flow path of the liquid-vapour fluid mixture. This flow augmentation induces a thermal boundary layer mixing effect, which enhances the convection heat transfer within the system under thermal loading. A multiphase numerical simulation model is developed to simulate the fluid phase change and wall temperature distribution of a two-phase closed thermosyphon. The Lee model is adapted to calculate mass and energy transfer source terms during the condensation and evaporation phase-change processes, while the Volume of Fluid method is employed to track liquid-vapour interface movement. The analysis of the new design reveals that the vortex generator has the most significant impact on average wall temperature distribution and overall thermal resistance when it is positioned in the adiabatic section and condenser section of the thermosyphon body. The reduction in thermal resistance is 3.5% and 3.3% when positioned in these two sections, respectively. This reduction corresponds to a higher velocity of the liquid-vapour mixture flow in these regions, indicating that thermal boundary layer mixing can be most enhanced in regions where the liquid-vapour mixture flow velocity has a higher magnitude.