Impact Of Gedeon Streaming On Thermo-Acoustic Conversion Effect And Corresponding Suppression Method

Thermoacoustic engine,powered by thermoacoustic effect,can convert thermal energy into mechanical energy.It is considered as an attractive energy conversion machine due to its high reliability and longevity as it operates without moving components.For decades,breakthrough progresses have been made in both thermoacoustic theory and thermoacoustic engine prototype.The traveling-wave thermoacoustic engine has a higher theoretical efficiency due to perfect thermal contact between working fluid and solid boundary in the regenerator,thus becoming more sought-after.However,an acoustic streaming named as Gedeon streaming may occur in the close-looped configuration of the traveling-wave thermoacoustic engine,and has a detrimental influence on the system thermal efficiency.In order to explore the mechanism of Gedeon streaming,and to restrain it,following theoretical and experimental studies have been carried out:(1)The influence mechanism and the characteristic of Gedeon streaming on the thermoacoustic conversion effect in regenerator are analyzed.The newly developed four-stage traveling-wave thermoacoustic engine and the double-inlet pulse tube cooler have been simluated based on thermoacoustic theory.According to the simulated results,the influence mechanism and the characteristic analysis of Gedeon streaming have been discussed.The emphasis is put on the fact that the energy flow rate carried by the Gedeon streaming is a function of local temperature,and in turn the temperature gradient is significantly dependent on the energy flow rate carried by the Gedeon streaming.The results indicate that the varying temperature profile inside the regenerator,caused by the various amount of Gedeon streaming,is the mechanism beneath the effect of Gedeon streaming on the thermal efficiency.(2)The impedance characteristic and the time-averaged pressure drop induced by the jet pump in oscillatory flow are analyzed.The jet pump,which can induce the time-averaged pressure drop,has been used in thermoacoustic engines to suppress the Gedeon streaming.The characteristics of the oscillatory flow field in the jet pumps with rounding edge and sharp edge and the adjacent region have been numerically simulated.Based on the simulated results,an experimental apparatus has been set up to analyze the time-averaged pressure drop induced by the jet pump and its dependence on the jet pump’s configurations(including the dimensionless rounding at the edge of the small opening,the taper angle and the cross-sectional area ratios)and state parameters(including the frequency and the charged pressure),as well as its working efficiency.The experimental results and analysis provide the guidance for jet pump.The analysis imply that the jet pump with sharp edge can be more promising to induce the time-averaged pressure drop.Therefore,the traditional understanding that rounding the edge in small opening is beneficial to increase the time-averaged pressure drop could be ambiguous.However,rounding the edge could improve the working efficiency,due to the significant decrease of pressure drop in the diverging direction.Meanwhile,the application of quasi-static hypothesis for the jet pump in oscillatory flow is discussed.(3)The experimental research on the suppression of Gedeon streaming by jet pump in the traveling-wave thermoacoustic engine is carried out.Taking four-stage traveling-wave thermoacoustic engine as the research object,the jet pumps with sharp edge and rounding edge are used in the system to suppress the Gedeon streaming based on the evaluation of the influence of Gedeon streaming.Compared with the theoretical Gedeon streaming,it is found that the Gedeon streaming in the system is much larger and the direction is converse,because of the existence of the conical tubes at the variable sections of the four-stage traveling-wave thermoacoustic engine.According to the characteristics of the four-stage traveling-wave thermoacoustic engine,the time-averaged pressure drop of the jet pump is predicted.The prediction method is verified by comparing with the experimental value,and the jet pump is designed based on the predicted time-averaged pressure drop.When the single stage heating power is 700 W,the pressure amplitude is increased by 17.8%after the designed jet pump is introduced.In the case of driving RC load,it is shown that when the load is 1.16×10g-2.98×107i Pa·s/m3,the thermal efficiency is increased by 64.9%with the Gedeon streaming suppressed by the jet pump,and the corresponding relative Carnot efficiency is increased by 57.3%.