Numerical simulation of stages number influence to the characteristics of a looped tube thermoacoustic Stirling engine

Background and Objectives: The traveling wave thermoacoustic engine is a variation of the Stirling engine family. With an increase in the number of stages of a traveling wave thermoacoustic engine from one to four, an improvement in the characteristics of the acoustic wave in the regenerator zone is observed, the temperature difference between the heat exchangers required to start the engine decreases, and the efficiency increases. For this reason, it is important to study the patterns of changes in engine characteristics with a further increase in the number of stages. The aim of the work was to study the influence of the number of stages on the characteristics of the acoustic wave in the engine. Materials and Methods: A numerical calculation of eight models of engines with the number of stages from three to ten was carried out in the Delta EC program. The working gas is argon under a pressure of 1.5 MPa, the diameter of the heat exchangers is 160 mm, the diameter of the acoustic resonator is 41.2 mm, the length of the looped engine resonator for all models was 8 meters. The stages in all engines were structurally the same. In the course of the calculations, the number of stages and the number of acoustic loads changed, while maintaining the same total length of the hull-resonator. For each of the eight models studied, the acoustic load was optimized to achieve the maximum engine efficiency. Conclusion: It was shown that with an increase in the number of stages from three to ten, there is a gradual increase in the phase difference between the pressure and velocity oscillations, that is, the wave approaches the parameters of a standing wave in the entire cavity of the resonator. In this case, the maximum acoustic load power and efficiency were observed when the number of stages was equal to five. With an increase in the number of stages from five to ten, the power of each individual stage decreased by 15.8%, and the efficiency decreased by 8%.