Thermal Performance of a 140–200 K Grooved Heat Pipe Under Different Orientations

An omega-shaped grooved heat pipe charged with ethylene was fabricated to meet the heat dissipation requirement for the temperature range of 140–200 K over a long distance. The thermal performance of the heat pipe was experimentally investigated in both horizontal and vertical orientations. Results show that the ethylene heat pipe was able to transfer 20 W of heat over 0.9 m with a temperature difference below 5 K for the entire 140–200 K temperature range when placed horizontally. When positioned vertically with the condensation section above the evaporation section, the heat pipe operated successfully within the temperature range of 160–200 K under the same heat load. However, when the working temperature decreased to 140 K, the temperature difference became larger. Additionally, temperature oscillation was also observed at 140 K. The difference in the thermal performance of the heat pipe under the two operating orientations and the heat transfer anomaly were theoretically analyzed, and suggestions for future improvement of the heat pipe design were also proposed.