A high frequency cascade thermoacoustic engine

A miniature cascade thermoacoustic engine, which consisted of one standing-wave stage and one traveling-wave stage in series, was built and tested, which length was about 1.2 m, operating at 470 Hz using helium as working gas. The cascade modeling, the simulation and the primary experimental results are described in this paper. Four different configurations of the miniature cascade thermoacoustic engines had been designed and compared. According to the analysis, the diameter ratio of stages was designed to extend the traveling-wave region, which optimized value was about 1.69. The peak-to-peak value of the acoustic pressure was predicted to arrive to 3 bar at the 3 MPa mean pressure of helium when 300 W heating power was the input. The features of the engine were predicted delivering 68 W acoustic power with a thermal efficiency of up to 22.74% (the ratio of acoustic power to heater power). Due to careful designing, the engine self-excited the oscillation smoothly from the first experiment. An onset temperature gradient of about 4.5 K/mm was achieved, and the peak-to-peak acoustic pressure was 48 KPa at the 2 MPa mean pressure when 200 W heating power was the input. The design computation and experimental results showed a rather good agreement between the measured and calculated pressure phasor and temperatures distributions in the cascade thermoaoustic engine.