| Thermoacoustic efficiency is limited by inherent thermodynamic irreversibility in standing-wave thermoacoustic engine, by the serious viscous loss because of the low acoustic impedance in traveling-wave thermoacoustic engine, and by the Gedeon streaming loss in thermoacoustic-Stirling hybrid engine. To eliminate Gedeon streaming and to get more acoustic power on higher efficiency level, the newly discovered another hybrid thermoacoustic engine is the cascade combination of standing-wave and traveling-wave engines. And more extensive commercial applications for low frequency thermoacoustic engine are restricted by the bigger size and less-compactness. So this theme aimed on how to realize the miniaturization of cascade thermoacoustic engine. According to the buildup and control of acoustic field, thermoacoustic network theory, system and cybernetic viewpoint, the basic investigation and the manufacture of the cascade thermoacoustic engine prototype and it drove tandem thermoacoustic refrigerator were developed exploring. The innovative investigation in this dissertation were mainly described as below,1,The dynamic complexity was increased by the coupling among different thermoacoustic units, such as the difficulties in understanding of its mechanism, building calculation model and tuning or controlling the system. It was necessary to breach the traditional linear thermoacoutic theory solving the complex thermoacoustic system. According to the direction of the developed thermodynamic theory and the method of thermoacoustic network analysis, the sound field and separated-parameter model was analyzed, including of theory study, numerical simulation and experimental study, which would also contribute to the development of thermoacoustic network theory.2,The tuning of the character of traveling-wave phasing and high impendence in regenerator was the key technique to realize cascade thermoacoustic system. The difficult issue was to determine the location and the length of the high impedance traveling-wave region. According to the development of thermoacoustic network theory and the analysis on total system network, the phasing-tuning mechanism of local compliance impedance in regenerator and external inertial and resistance impedance was discovered. The linear network analysis and experiments on the tuning of the location and length of the traveling-wave region was performed using acoustic impedance-tuning method. The character impedance in the acoustic route outside of regenerator could vary the phasing in regenerator effectively. This developed the academic idea on phasing-tuning in regenerator.3,The coupling character among the standing-wave stages and traveling-wave stages was the special complicated issue in cascade thermoacoustic system. Orthogonal experiment design and variance analysis were adopt to investigate the coupling character on heating powers between stages in the cascade thermoacoustic engine. This breached the traditional experimental methods in investigating thermoacoustic system. The coupling character influencing factor between stages'heating powers was extracted. The optimum ratio of the heaters power between stages was obtained from experiments.4,The cybernetics was introduced into thermoacoustic network theory. To well predict the onset temperatures, the control system model of the cascade thermoacoustic engine was built and calculated, based on cybernetics, system analysis and wave propagation laws, which greatly improved calculated precision.5,According to the self-organization theory, the double onset and thermoacoustic instability phenomena in experiments were analyzed. The important influencing parameter was distinguished from experiments.6,The tandem thermoacoustic refrigerator, driven by the cascade thermoacoustic engine, operating on the icebox temperature, which had high cooling power density (20W/cm2) and bigger COP (1.43), was designed and explored in experiments. The operating mode and multi traveling-wave region were well controlled and tuned.
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