Experimental study on transient heat transfer performance of high temperature heat pipe under temperature feedback heating mode for micro nuclear reactor applications

The use of heat pipe-cooled micro nuclear-powered reactors (HPNRs) is crucial for shaping a low-carbon energy structure in the future. However, there is still a lack of experimental investigations on the transient heat transfer performance of high-temperature heat pipes (HTHPs) under the application of HPNRs. To address this issue, a hardware-in-the-loop (HIL) test platform has been developed to dynamically adjust the heating power of the heat pipe in real-time considering the temperature feedback (TF) effect. A horizontal test rig composed of a hex block, a sodium heat pipe, and six electric heaters has been built in the laboratory, and its thermal effectiveness has been evaluated at 60%. Subsequently, a transient HIL test under the TF heating mode has been conducted. The results show that the frozen start-up of the HTHP can be divided into five stages based on the power exponential growth rate and the state of the sodium vapor. During the transient start-up process, the worst axial heat transfer of the HP occurs when the front of the continuum vapor arrives at the adiabatic section, where the maximum thermal resistance is 500 K/W. Heat pipes with a high filling ratio can avoid integral overheating of the evaporator when occurring viscosity limit at the start-up period. Different time scales of neutron growth and thermal inertia cause alternating oscillation of power and temperature. This work provides valuable insights into the transient heat transfer behavior of the HTHP under the running process of the HPNR system.