Transient experimental and numerical study of thermosyphon under different heating fluxes and filling ratios

A transient thermosyphon model was proposed to meet the growing demand for complex thermal protection requirements. The primary goal of this work is to build a reliable, and engineering-approach simulation tool to capture the transient characteristics of the thermosyphon, which is blank in existing literature. With calculation of net vapor production, the transient performance can be predicted, including the temperature distribution, pressure distribution, startup time, etc. The predicted results by the model showed good agreement with the experiment results of the thermosyphon, and the overall error was verified to be within 10 %. The study investigated the steady-state, transient startup, and working condition switching processes with various heat fluxes and filling ratios. The model-derived saturation temperature and pressure of the thermosyphon over time aligned consistently with the experiments. In addition, by leveraging the visualization advantages of the CFD method, it has been confirmed that a low filling ratio can result in a severe overheating issue in the upper region of the evaporation section. It was observed that by augmenting the heating input, the equivalent thermal resistance of the thermosyphon with a 50 % filling ratio and the heating power of 600 W was reduced to its minimum value of 0.0291K/W. The maximum effective thermal conductivity can increase to 3.75×10⁴W/m·K.