| Energy and environmental problems are the long-term "bottleneck" that restricts China’s economic and social development,and the development of low-grade waste heat utilization technology is a major demand for the implementation of China’s energy conservation and emission reduction strategy,which is related to the construction of a beautiful China and a new era of ecological civilization.Thermoacoustic heat engine is a new type of thermal power conversion device.The working principle is that through the thermoacoustic effect,heat energy is directly converted into sound energy,so as to achieve the purpose of low-grade heat energy utilization.No harmful substances emission,no mechanical moving parts,high thermal efficiency,good reliability and long life are its advantages.However,to promote the engineering application of thermoacoustic heaters,there are still many problems to be solved.Most of the current studies related to multi-stage loop traveling wave thermoacoustic heaters are basically about the thermoacoustic nucleus in a centrally symmetric position or some special positions,and this decentralized arrangement is objectively unfavorable to the utilization of thermal energy and seriously hinders the engineering application of thermoacoustic heaters systems.The research object of this thesis is mainly a two-stage traveling wave thermoacoustic engine,and the research mainly focuses on its defects and shortcomings in the utilization of heat energy at low temperature,exploring its performance in the utilization of low-grade heat and the maximum depth of possible utilization of low-grade heat,and making technical reserve for the engineering application of thermoacoustic system,mainly doing the following research work.In this thesis,based on the basic theory of linear thermoacoustics and modern acoustics foundation,a simulation model of a two-stage traveling wave thermoacoustic heat engine is constructed by applying the linear thermoacoustic coding program Delta EC.Combining the numerical simulation results and introducing relevant acoustic theories for analysis,it is found that in the typical acoustic field distribution of the loop traveling wave acoustic system,there are four pure traveling wave points about 1/4 wavelength apart,and such pure traveling wave points are ideal locations for the arrangement of thermoacoustic cores.A scheme to adjust the sound field within the loop thermoacoustic heaters by changing the position of the thermoacoustic cores to establish boundaries is proposed.Different thermoacoustic core positions can adjust the sound field inside the loop thermoacoustic machine,and the reasonable choice of the thermoacoustic core installation position and the reasonable design of each component can achieve a good acoustic impedance matching.For a thermoacoustic system with two thermoacoustic cores,an arrangement interval of 1/4 wavelength may be the best arrangement.The system was designed and built with seven different thermoacoustic heat engine systems with resonant tube ratios（the ratio of pipes used to connect two thermoacoustic cores）of 1:1,1:1.5,1:2,1:2.5,1:3,1:3.5,1:4,etc.The experimental study was carried out using the control variable method,and the following experimental results were obtained:firstly,the asymmetric two-stage loop thermoacoustic engine,the best position of the thermoacoustic nucleus exists,i.e.,the resonant tube ratio is 1:3.5,and the distance between the two thermoacoustic nuclei is about 1/4 wavelength;the performance of the seven types of loop thermoacoustic heat engine was analyzed and compared,and the starting temperature difference was as low as 59.6℃ when 2.5MPa N2 was used as the working mass and the resonant tube ratio was 1:3.5.Compared with the symmetrical two-stage loop thermoacoustic engine,the starting temperature difference is reduced by about 93.4℃. |
