Numerical study and sensitivity analysis of heat transfer characteristics of heat exchangers in a high-power free-piston Stirling generator

The increasing of deep space exploration missions has promoted research on space nuclear power systems worldwide. Stirling generators, especially free-piston Stirling generators (FPSGs), are a promising dynamic energy conversion technology for space nuclear power systems. As core components of a Stirling system, oscillating flow heat exchangers (OFHXs) have a crucial impact on the performance of the system. Unfortunately, a comprehensive comparison between low-order numerical models and the computational fluid dynamics (CFD) simulations on the engine core unit (ECU) is lacking. Meanwhile, the heat transfer characteristics of the ECU at high power levels remain poorly understood. Therefore, in this paper, a 10 kW FPSG is taken as an example, and its ECU is numerically simulated using Sage software and CFD simulation, respectively. Then the results of the two different numerical methods are compared under rated conditions, and we concluded the Sage model can effectively characterize the heat transfer distributions within the ECU. Furthermore, the heat transfer characteristics of the ECU were analysed in detail using the Sage model. The results indicate that a 90° change in the acoustic phase difference of the ECU could lead to a 32 kW variation in acoustic power of the high-temperature heat exchanger (HHX), and the regenerator transitions from amplifying acoustic power to beginning to consume acoustic power. This demonstrates that the heat transfer characteristics of the OFHX are sensitive to the distribution of the acoustic phase difference. This work contributes to the development of the ECU for high-power FPSGs, which will strengthen the foundation for their subsequent integration with micro nuclear reactors.