Experimental Study On Gravity-effect for Startup Performance of High-Temperature Sodium Heat Pipe

The gravity-effect plays important factor on the startup and thermal performance of high-temperature heat pipes (HTHPs). But the results of past studies are quite different and confusing our perception. In this paper, a sodium HTHP is fabricated and experimented to study the gravity-assisted, horizontal and anti-gravity three modes on the startup behaviors and quasi-steady thermal performance. The HTHP is designed to phi 25 x 410 mm, two wraps of 100 mesh screen, and filling mass of 15 g sodium. The HTHP is tested at the inclination angle of 0 degrees, 90 degrees, -30 degrees and -90 degrees. The results show that no startup failures are found during all the three operating modes and the startup time for HTHP fully starting at different inclination angle is the same as 10 min. However, the gravity-effect cannot be ignored and plays important influence on the HTHP startup. Compared with the horizontal mode, the gravity-assisted mode (90 degrees) is beneficial for the starting more favorably and decreasing the temperature difference between the evaporator and condenser after the startup. The anti-gravity working mode has a significant adverse effect on the temperature rise-rate of the HTHP condenser and increase the temperature difference after the startup in a large step as the inclination angle changed from 0 degrees, -30 degrees to -90 degrees.