Investigation On Onset Process Characteristics Of Travelling-Wave Thermoacoustic Engines

Traveling wave thermoacoustic engine,which is capable of using low grade thermal energy,has great advantages of high efficiency,high reliability,simple structure and low cost.It is expected to be applied in the fields of industrial waste heat recovery,solar power generation and distributed energy supply,etc.Due to the requirements of lower onset temperature,higher acoustic power output and higher energy density,traveling-wave thermoacoustic system with multi-thermoacoustic cores has been paid more and more attention.The research on the performance and mechanism of traveling-wave thermoacoustic system with multi-thermoacoustic cores(ie,multi-stage traveling-wave thermoacoustic system),such as onset characteristics and working mechanisms of the coupling of different thermoacoustic cores,is still lacking.In order to reveal the dynamic onset process characteristics of traveling-wave thermoacoustic engines,the engines can utilize low-temperature heat source efficiently.Onset characteristics of the thermoacoustic Stirling engine and multi-stage looped traveling-wave thermoacosutic engines are studied in this paper.Details are as follows:1.Based on the linear thermoacoustic theory,considering the acoustic resistance,acoustic inertance,acoustic compliance and thermal-relaxation effects of the components in the system,a time-domain network model suitable for traveling-wave thermoacoustic engine is developed.And the numerical simulation on onset characteristics of the traveling-wave thermoacoustic engine is developed.In this paper,the reliability of the model is verified by comparing with the experimental results of the thermoacoustic Stirling engine from the angle of the onset temperature and the quality factor.The model can accurately predict the onset characteristics of the engine and describe the acoustic power generation and disspation in the thermoacoustic Stirling engine below the onset.2.The time-domain network model for multi-stage traveling-wave thermoacoustic engines is developed and the research on onset characteristics of the engines is carried out.In this paper,the reliability of the model is verified by comparing with the experimental results.Afterwards,the traveling-wave thermoacoustic engines with different stages were designed by DeltaEC and their time-domain network models are established.Onset temperatures,frequencies,quality factors are obtained and analyzed.The results show that the quality factor of the three-stage traveling-wave thermoacoustic engine is higher than that of the four-stage and six-stage traveling-wave thermoacoustic engines,which is in agreement with the conclusion that the three-stage traveling-wave thermoacoustic engine has the best single-stage performance in DeltaEC model.3.A three-stage traveling-wave thermoacoustic engine is optimized and the output acoustic impedance of the three-stage traveling-wave thermoacoustic engine is analyzed theoretically.When the imaginary part of the output acoustic impedance is under the order of 10~7Pa s/m3 and the real acoustic impedance range is between 3×10~7-4×10~7 Pa·s/m3,the output acoustic power and thermo-acoustic efficiency are high.The highest single-stage acoustic power is 4006 W and the thermal-to-acoustic efficiency is 28.2%.This is a good guide for the further acoustic matching between the traveling wave thermoacoustic engine and the linear alternators.