Experimental study on the operating characteristics of high-temperature heat Pipe–Stirling thermoelectric conversion systems

This study experimentally investigates the operating characteristics of a high-temperature heat pipe–Stirling thermoelectric conversion system. A 600 W test platform was established to examine the coupling behavior between an alkali-metal heat pipe and a dual-opposed free-piston Stirling generator (DO-FPSG). Two configurations were compared: a Direct-Heating Stirling Thermoelectric Conversion System (DH-STC) and a High-Temperature Heat Pipe-Coupled Stirling Thermoelectric Conversion System (HPH-STC). Experiments were conducted under identical working fluid pressure, cooling, and electrical load. Most previous studies on heat pipe–Stirling systems focused on numerical simulations and theoretical analysis. This work provides the missing experimental evidence and quantitative data, giving direct insight into the real coupling behavior. The heat pipe introduced strong thermal inertia, which increased the onset temperature and extended the startup duration. At steady state, the HPH-STC system delivered 30–40 % less output power and 7–10 % lower efficiency than the DH-STC system. The decrease mainly resulted from additional thermal resistance and interfacial heat losses at the coupling interface. The heat pipe maintained a stable axial temperature gradient. This confirms that its heat-transfer performance is reliable and consistent. Model validation showed that the classical adiabatic analysis accurately predicted the dir ect-heating behavior but deviated under heat-pipe coupling. This deviation highlights the need to incorporate distributed thermal resistance and non-ideal heat-transfer mechanisms into the model. The results provide systematic experimental evidence and quantitative data on HPH-STC system operating characteristics, and they offer guidance for future applications in space nuclear power and distributed energy conversion.