Theoretical and experimental study of free piston Stirling generator for high cold end temperatures

The cold end temperature of the free piston Stirling generator (FPSG) should be increased to reduce the heat sink radiator area for space application. A comprehensive model coupled with thermodynamics, dynamics, and electromagnetism was built and solved numerically to investigate the intrinsic relationship between cold end temperature and FPSG performance. It shows that, with fixed heating power, as the cold end temperature increases, the magnetic field strength of alternator air gap decreases. The output power and efficiency show a steadily declining trend. A 100W prototype was tested for model verification. The relative error between experiment and model prediction of the amplitude of piston and displacer is 2.48 % and 11.97 % respectively. For phase difference between piston and displacer, thermal efficiency, and working frequency, the relative error is 54.32 %, 27.23 %, and 2.39 % respectively. When the cold end temperature rises from 320.5K to 394K, the output power and efficiency relative error is 26.06 %∼37.85 % and 27.67 %∼34.24 % respectively. The predicted parameter effect trend is well consistent with experiment, showing the important guiding role for generator optimization operating at high temperatures. The exergy analysis shows that increasing cold end temperature causes input exergy decline and aggravates exergy loss, which is main cause of generator performance degradation.