Phase adjustment analysis and performance of a looped thermoacoustic prime mover with compliance/resistance tube

To realize high normalized acoustic impedance and near travelling-wave acoustic field in the regenerator is the key issue for a thermoacoustic engine to be driven by low-grade heat (e.g., waste heat, geothermal energy and solar thermal energy, etc.), and a looped thermoacoustic system with the appropriate acoustic field is considered one of the promising techniques. The present work analyzes the conception and mechanism of the phase adjustment in a looped structure, based on which two phase adjustors (namely compliance tube and resistance tube) are introduced to build appropriate acoustic field. Systematic experiments have then been conducted on a looped thermoacoustic prime mover with compliance/resistance tube, and the results show that the system with appropriate compliance/resistance tube can be initiated to oscillate at quite low heating temperature, indicating the phase adjustor can help to build up proper acoustic field. The lowest onset temperature is 40 °C, with a compliance tube and using the CO2 of 2.37 MPa as working fluid. Features of the acoustic field, including pressure amplitude, volumetric velocity amplitude and their phase difference, have also been numerically analyzed to verify the phase adjustment mechanism. Besides, the influence of its installation position and length of the compliance tube on the performance of the prime mover has been experimentally and numerically studied. Finally, a comparison is made to analyze the similarity and difference between the performances of compliance tube and resistance tube for phase adjustment.