Design and optimization of two stage annular thermoelectric generator coupling with high temperature heat pipe application

• A novel two-stage ATEG coupling with high temperature heat pipe was designed and optimized. • Effects of detailed geometric parameters and contact resistance on thermoelectric conversion were analyzed. • Detailed structural design and optimization were conducted for ATEG coupling with heat pipe. Traditional energy sources have limited applications in deep space and deep-sea exploration as they cannot provide a long-term, reliable energy supply. Small nuclear reactors are ideal because of their high adaptability and long life, especially for powering deep space missions. This study focuses on integrating thermoelectric generators (TEG) with small nuclear reactors. Due to the limitation of conventional planar thermoelectric devices in conversion efficiency, a novel annular thermoelectric device (ATEG) is proposed and discussed. Compared with the traditional flat thermoelectric devices, annular thermoelectric devices have the advantages of larger contact area with heat source, smaller volume and stable heat flux. According to the application requirements of heat pipe reactor, the geometric parameters of thermoelectric conversion system are optimized in order to find the best geometric parameters and external load resistance. Through detailed investigation, we found that under certain conditions (such as 900 K hot end temperature and 10 mm device height), the single-stage SKD thermoelectric device can achieve the highest conversion efficiency of 8.99 %. Optimizing contact characteristics (e.g., surface roughness less than 2 µm, contact resistivity less than 10 microohms square centimeters) is critical to maintaining this high level of efficiency. Based on the thermoelectric characteristics of single-stage thermoelectric devices, two-stage thermoelectric devices are studied. The two-stage SKD-BT device exhibits better performance. When the height ratio of thermoelectric material is 0.7, the efficiency of the two-stage SKD-BT device is as high as 11.49 %, which is 27.8 % higher than that of the single-stage thermoelectric device. In this study, two innovative ways of integrating cascaded annular thermoelectric devices are proposed, which are simple in structure and easy to be modularized. Under the same temperature boundary condition, the thermoelectric conversion efficiency of the PN leg alternating connection structure can reach 10.95 % under the optimal load resistance, which is better than 6.45 % of the parallel connection structure.