Operational characteristics of a free-piston Stirling generator with resonant self-circulating heat exchangers

Heat transfer is one of the most critical issues faced by free-piston Stirling generators (FPSGs) during power amplification, and the emergence of resonant self-circulating heat exchangers offers an alternative solution. In this study, a high-power FPSG with resonant self-circulating heat exchangers has been numerically studied using commercial software SAGE and thermoacoustic post-processing. The principle feasibility and operational characteristics of the proposed system with different loop lengths are verified based on comparative analysis with the Component Test Power Convertor. Results show that introducing a self-circulating heat exchanger can achieve high-power heat transfer through a steady flow. However, it results in a significant degradation in the performance of the FPSG, where the acoustic power loss in the loop is the most critical cause. The pump used to generate the steady flow also requires additional power consumption. Furthermore, systems with shorter loops of non-integer multiples of wavelength have higher system efficiency and lower pump power consumption. For example, the output electric power can achieve 9.9 kW (corresponding to a thermal-to-electric efficiency of 18.8%) when the loop length is 2 m, where the power consumption of the pump is only 0.19 kW. Meanwhile, the pipe diameter of the loop and the temperature difference between the inlet and outlet of the high-temperature heat exchanger should be determined by considering both the performance of the FPSG and the power consumption of the pump.