Research Of Thermoacoustic Mechanism And A Thermoacoustic Refrigerator By Double Acoustic Drivers

Due to advantages of high reliability,being environmentally friendly,low energy requirement,and especially having no?or few?movable parts,thermoacoustic engines?refrigerators?,a new energy conversion equipment,has great potentials in dynamical engineering,new energy utilization,refrigeration and cryogenic engineering,and modern vehicles?such as aerospace vehicles,ships,submarines,etc.?.In recent three decades,thermoacoustics,including thermoacoustic engineering,gains popularity from scholars and engineers,and becomes a hot research area of power engineering and engineering thermal physics.Nonlinearity of thermoacoustic effect makes its mechanism extremely complicated.The nonlinearity effects such as onset,frequency-selecting property,oscillationmode,stability,mass acoustic flow,and time-averaged energy of thermoacoustic system cannot be explained by traditional linear thermoacoustic theory.Therefore,the development of nonlinear thermoacoustic theory is needed in thermoacoustic engineering.On the other hand,other applications require the development of new-type thermoacoustic equipment to satisfy engineering demand and commercialization.The purpose of this dissertation is to combine the development of the nonlinear theory of thermoacoustic device and design of a new thermoacoustic refrigerator by double acoustic drivers,to explore the spontaneous oscillation substance of thermoacoustic system,to explore controlling parameters of thermodynamic process,and to lay the foundation of engineering application of thermoacoustic engines?refrigerators?.This dissertation includes the following aspects:?1?Solving thermoacoustic ordinary differential equation system by using Galerkin's low spectrum mode,and found time periodic solution,and further,phase trajectories?phase diagrams?of the pressure signals and the temperature signals,and discussed preliminary principals of thermoacoustic spontaneous oscillation.The result shows:Stable solution of thermoacoustic system is nonlinear time periodic oscillation that possesses stability of limit ring.?2?Starting from basic fluid governing equations,nonlinear parameter oscillation equation of thermoacoustic system is derived.Based on the network analysis of this equation,a parameter oscillation network model of thermoacoustic system is built.This network consists of a time-varied sound capacitance,a sound inductance,a nonlinear sound resistance,and a pump source.This model is consistent with above nonlinear parameter oscillation equation.By using“average value”method,nonlinear parameter oscillation equation?or above network equation?is solved.Stability of thermoacoustic oscillation that is described by limit ring is analyzed by using Lyapunov function method.And conditions of stable periodic movement for thermoacoustic system are found.The result shows that the acoustic oscillation of thermoacoustic network depends on stimulations of time-varied sound capacitance parameters.?3?The method of the quantum thermodynamics is employed to analyze the performance of a quantum thermoacoustic micro-cycle.The evolution of each thermal phonon has to satisfy the Schr?dinger equation in quantum mechanics.The quantum mechanic model of the thermoacoustic micro-cycle is established.The quantum thermoacoustic micro-cycle consists of two constant force processes and two quantum adiabatic processes.The quantum thermodynamical behavior and evolution of the thermal phonon in a one-dimensional harmonic trap are investigated based on the Schr?dinger equation and the two-eigenstates system.The energy eigenvalue of the thermal phonon are employed.The quantum thermoacoustic micro-cycle is derived by considering Gibbs probability distribution.The optimal relationship between the dimensionless power output P*versus the thermal efficiency?is obtained.The analysis shows that both the power output and the thermal efficiency decrease along with increases of the width L₁ of harmonic trap.One can find that the characteristic curve of P*-?is parabolic-shaped one.There exist a maximum dimensionless power output P*and corresponding frequency?.It is noteworthy that there is a critical temperature gradient for the quantum thermoacoustic micro-cycle.The critical temperature gradient is important because it is the boundary between the heat engine and the heat pump.The optimal design and these operating conditions for the quantum thermoacoustic micro-cycle are determined.The results provide a new method for studying the thermoacoustics by means of the quantum thermodynamics and broaden the applied range of the quantum thermodynamic.?4?Basic concepts and description methods of fluid network are discussed.Starting from basic governing equations of thermoacoustic system,network model of different parts of the thermoacoustic refrigerator by double acoustic drivers is built,and coupling matrix of model of different parts is found.The entire network model is built based on network models of different parts.?5?A thermoacoustic system is a self-organizing system.The collective feature of a self-organizing system can be recognized from the behavior of its pattern.A theoretical study for features of pattern of the thermoacoustic system by double acoustic drivers is performed.Starting from analyzing sound pressure of each part of the entire device,and by adopting“Quartet Logic”method,coherent coupling effect between two coherent states is analyzed.According to the pattern condition,pattern matrix,coupling matrix,structure vector and collective feature of the pattern are found,and eventually,the collective feature of the pattern of the entire system is given by an analytical expression.Numerical example leads to the relation between the collective feature and other parameters.?6?A thermoacoustic refrigerator by double acoustic drivers is designed and built.Optimal selections of structure parameters of different parts,structure parameters of entire device and thermoacoustic acoustic field is made according to thermoacoustic theory and experiences in researching in thermoacoustic devices.Relations between the refrigeration temperature difference of it and the parameters such as phase displacement of two sound sources,locations of regenerator,frequency and amplitude of acoustic wave are experimented and researched.