Investigation Of The Oscillation Mechanism And Thermodynamic Optimization Of A Standing-wave Thermoacoustic System

Thermoacoustic engine is a new type of energy device, which can transform heat intoacoustic power, or vice verse. The former is thermoacoustic prime mover, and the latter isthermoacoustic refrigerator. It is a totally free-moving refrigerator if a thermoacousticrefrigerator coupled with a thermoacoustic prime mover. In that ways, it is an importantsignificance to research the operate mechanism of thermoacoustic prime mover. It is theonset process that the state from static to operate normally of thermoacoustic prime mover,which is also the process of building self-excited oscillation. It is helpful to have a betterunderstanding of thermoacoustic effect by research the self-excited oscillation mechanismof thermoacoustic prime mover. On the based of understanding and summarizing thethermoacoustic theories comprehensively, the self-excited oscillation mechanism ofstanding-wave thermoacoustic prime mover are analyzed on the aspects of network theory,dynamics and thermodynamics. And the influence of pressure on the threshold temperature,which is the temperature that maintains the self-excited oscillation of thermoacoustic primemover, are analyzed in the experimental investigation.The main researches include the following sections:On the based of the thermoacoustic distributed parameter network model, the networkstructure of each thermoacoustic component and the whole thermoacoustic prime moverare built by derived the network admittance matrix of each thermoacoustic component.Compared the thermoacoustic network with the electric network, the power flux whichinput the whole network are calculated by use the Hermitian form. In the network, powerflux balance means building self-excited oscillation. On the based of that, the closed loopnetwork of the whole thermoacoustic prime move has been broken into a two-port openloop network, and the threshold temperature and operation frequency are calculated on thecondition of the imaginary part of angular frequency equals to zero. And the calculationalresults are shown to be in good agreement with the experimental results.The stability of thermoacoustic system is investigated on the aspect of dynamics. Theautonomous equations of the the first order disturbed quantities are derived on the based of the basic equations of thermoacoustic self-excited oscillation system. The stationary statepoints of the autonomous equations are calculated, and the stability of the stationary statepoints are analyzed by using Lyapunov stability theory. The dynamic behavior of thestability versus time evolution in building self-excited oscillation process is described byusing several concepts in chaos dynamics.Reducing the energy loss in thermoacoustic prime mover system is helpful to reducethe threshold temperature, and enhance the ability of utilizing low-grade energy. Thesymplectic symmetry feature of the distributed parameter network transferring matrix ofeach thermoacoustic component are analyzed. Based on that, the minimum eigen-impedance is analyzed with utilizing the Rayleigh quotient. In the thermoacoustic network,the minimum eigen-impedance is corresponding the minimum network loss, namely, theenergy loss. The minimum limit of reducing the energy loss are given in the optimaldesigning of a thermoacoustic system, and the influence of operate conditions on theminimum network loss are investigated by numberical calculation.The performance of thermoacoustic self-excited oscillation on the thermodymamicspace are investigated on the aspect of thermodynamics. The thermodynamic cycle is atype of self-excited oscillation. The irreversible standing-wave thermoacoustic primemover and refrigerator thermodynamic micro-cycle which expressed as an ellipse in p-Vdiagram are built on the based of the oscillation feature of work fluid. The expressions ofcycle output power, thermal efficiency and cycle cooling load, coefficient of performanceare derived. The first law and the second law of thermodynamics performance and theecological function performance of the irreversible micro-cycle are investigated by usingthe method of finit-time thermodynamics.In the last part, the process of building self-excited oscillation are observed in ourthermoacoustic prime mover. The influence of pressure on the threshold temperature areinvestigated, and the calculational results are compared with the experimental results.