Experimental investigation on the heat transfer performance of high-temperature potassium heat pipe for nuclear reactor

Heat pipe cooled reactor (HPR) is considered as an excellent candidate for space power systems. As a core cooling method, the operational characteristics of high-temperature heat pipes need to be researched. In this paper, the heat transfer performance of potassium heat pipes (Φ30mm × 800 mm) is studied experimentally. The thermal behavior of heat pipe is tested under various conditions, including heating power (0.2–4 kW), air/water cooling method, inclination angle (0–90°), and filling ratio (20% and 100% of void in wick). And the characteristics of heat transfer limits are analyzed, consisting of dryout, entrainment, and sonic limit. The results show heating power is beneficial to heat transfer within the capillary limit. However, overheating occurs when heating power exceeds the capillary limit. The inclination angle has a strong effect on the thermal efficiency of heat pipe for the competition between gravity and entrainment, and the angle of 30° corresponds to the best thermal performance. Sonic limit and entrainment limit are estimated with a relative error of 38.7% and 17.9%. Dryout is divided into local dryout (<200 °C/m) and integral dryout (>200 °C/m). It is concluded that the high filling ratio (100%) and the small inclination angle (30°) are helpful to realize the optimal thermal performance. This work makes it possible to validate the operation of a high-temperature heat pipe and provides a reference for the design and application of HPR.