Experimental investigation on heat transfer performance of high-temperature thermosyphon charged with sodium-potassium alloy

Highlights: • A Na-K (wt. 55% K) thermosyphon is experimentally studied. • The periodic fluctuation of temperature occurs and finally eliminates. • Optimal working temperature is more than 700 °C for Na-K thermosyphons. • Heat source, condenser length and angle greatly affect performance of thermosyphons. Sodium-potassium alloy (Na–K), which is liquid at room temperature and pressure, is a promising working fluid for high-temperature heat pipes. Although several researches have been performed over the past decades, the experimental data for Na–K thermosyphons, especially for Na–K (wt. 55% K), was limited and needed. This study is to use Na–K (wt. 55% K) as working fluid to fabricate a high-temperature thermosyphon. The outside wall temperatures were measured to estimate the heat transfer performance of the fabricated thermosyphon by using 10 thermocouples, which were made of 0.2 mm-diameter Ni–Cr and Ni–Al wires. The thermal characteristics of the Na–K thermosyphon were studied at various heating temperatures (650, 675, 700, 725, 750, 775, 800, 825, 850 and 875 °C), condenser lengths (0.250, 0.220, and 0.190 m) and inclination angles (0° and 50°) to determine the influence of working conditions. Those factors considerably affected the heat transfer performance of the Na–K thermosyphon.