声学双作用型行波热声发动机的损失分析

本文根据经典热声学理论,对声学双作用型行波热声发动机系统进行了全面的损失分析。系统产生的损失可以分为内部不可逆损失与外部不可逆损失,其中内部损失可区分为:轴向漏热损失,流体黏性损失,不可逆传热损失与流动传热耦合损失。本文对一台效率为55.7%的声学双作用型行波热声发动机进行了具体的媚损失分析,结果显示,回热器与谐振管是产生损失最多的部件。谐振管中的损失主要是流动损失,而回热器中的流动损失则相对较少。     

热自然对流对热声起振行为的研究

主要研究热自然对流对热声发动机系统的影响。通过一系列的实验 ,发现热声发动机空间位置的变化对行波型热声机的起振温度、回热器的温度分布等重要参数有着相当大的影响。作者通过分析 ,对该现象进行了定性的解释。     

带阻性管的环路行波热声发动机性能研究

高效的行波热声发动机要求回热器处在接近行波和高声阻抗的声场。为此,本文拟采用阻性管进行调相,设计了一台单级环路行波热声发动机,分别以He,N2和CO2为工质,对该热声发动机的起振特性和稳态运行工况进行了系统的实验研究。结果表明,安装阻性管后,单级环路行波热声发动机的起振温度可以被降低300℃以上,最低起振温度仅为55C(工质为CO2,平均压力为2.35 MPa)。此外,系统可以在200℃以下的加热温度达到比较可观的压比。可见,阻性管可以作为环路行波热声发动机的一种有效调相方式,本文所提出的热声发动机系统具有利用低品位热源驱动的潜力。     

多段式回热器的斯特林热声发动机CFD仿真

热声回热器的温度梯度使得轴向气体存在不同粘性,因此单一水力直径的丝网会引起回热器的直流损失。为了减小该损失,文中提出了多段式回热器结构,建立了适用于大振幅下斯特林热声发动机的三维CFD计算模型。计算结果验证了多段式回热器能有效提高热声发动机的整机性能。该研究有助于增加对回热器的进一步认识和理解。     

行波热声发动机容腔管和反馈管的调相作用研究

带环形圈的热声发动机是一种新型的行波型热声发动机,由于能够在环形圈内回热器附近调制出行波相位,因此具有比驻波发动机更高的效率。环形圈的反馈管和180度弯管分别在系统中起着感和容的作用,在相位的调制过程中它们起着至关重要的作用,尤其是对于感的作用比较强的小型系统,它们的作用更加突出。该文通过计算,分析了小型行波热声系统中感和容对于回热器入口处和回热器中心位置处的压力波动和体积流率相位的调制作用,以及这种调制作用对于效率,压力波动的幅值的影响。     

行波型热声发动机起振温差的研究

热声机械作为一种新型的能量转化装置 ,讨论其起振温差对于利用低品位能源具有非常重要的意义。文中讨论了行波型热声发动机起振温差的计算方法 ,得到了回热器结构、工作介质、丝网、频率等对起振温差的影响规律     

直线电机驱动回热器性能研究

本文提出并搭建了一种采用直线电机驱动的回热器热声转换实验台,通过调节负载阻抗改变回热器处声场条件,研究回热器在不同声场下热声转换特性。文中首先对实验系统进行了数值模拟,结果表明,回热器存在最优的工作声场,但由于有限水力半径因素,最优声场会偏离行波相位。计算中系统获得了最大1300 W净输出声功,热声效率达到35%。之后进行的实验实现了回热器处声场的调节,验证了回热器的声功放大作用,并获得了与数值计算相同的趋势。     

自激振荡热声发动机的整机数值模拟研究

基于线性热声理论,以复频率作为迭代判据,给出具体的四端口网络模拟算法,对两台实际的热声发动机进行了整机数值模拟,并且结合实验结果进行了对比分析。计算结果证明它们的板叠和回热器分别处于驻波和行波为主要分量的声场中, 成为热声转换的核心。另外发现,频率误差不超过1％,相对振幅实验值约为计算值的70％,基本反映实验规律,同时解释了非线性影响是造成误差的主要原因。     

80 K温区的小型行波低温热声制冷机

热声制冷机由于结构简单、无运动部件,具有广阔的应用前景。本文在已有的小型行波热声发动机的基础上,开展了热声制冷的工作。利用线性热声理论对制冷机进行数值模拟,并对制冷机的各热声元件优化。优化后,系统整体装配横向尺寸仅0.5 m,在充气压力3 MPa,发动机输入功率384 W的条件下,达到了80 K的无负载温度。由于本制冷机由行波型热声发动机驱动,并且是通过线性热声理论优化,因此称之为小型行波低温热声制冷机。     

行波热声发动机声功输出特性研究

行波热声发动机具有效率高、可靠性好及环保等优点.本文分别以氮气和氦气为工质研究了行波热声发动机的声功输出特性.在平均压力为3.0MPa,输入功率为3000W时,氮气为工质获得最大492.3W输出声功,氦气为工质获得最大691.3W的声功.此外还针对两种不同锥度的锥形谐振管发动机的声功输出特性进行了对比研究.研究表明:设计合理的谐振管一方面能够有效降低加热温度,有利于利用低品位热源;另一方面还能有效地降低损失,在相同的加热量下具有更高的压比、更大的输出声功及效率.     

驻波热声系统的自激振荡机理

热声发动机的起振过程是一个产生并维持自激振荡的过程, 研究热声自激振荡机理有助于进一步了解热声效应的实质. 根据热声网络理论, 建立了驻波热声发动机的整机网络. 将热声网络比拟成电网络, 利用厄米特式计算了输入热声网络的视在功流, 功流平衡对应自激, 在角频率虚部为零的情况下计算了热声发动机的阈值温度和运行频率. 结果表明, 计算值与实验值符合得较好, 充气压力与阈值温度和运行频率的耦合关系大致相同. 所得结论有助于进一步探究热声效应机理以及热声发动机系统的优化设计.     

Theoretical prediction of the onset of thermoacoustic instability from the experimental transfer matrix of a thermoacoustic core

The aim of this paper is to propose a method to predict the onset conditions of the thermoacoustic instability for various thermoacoustic engines. As an accurate modeling of the heat exchangers and the stack submitted to a temperature gradient is a difficult task, an experimental approach for the characterization of the amplifying properties of the thermoacoustic core is proposed. An experimental apparatus is presented which allows to measure the transfer matrix of a thermoacoustic core under various heating conditions by means of a four-microphone method. An analytical model for the prediction of the onset conditions from this measured transfer matrix is developed. The experimental data are introduced in the model and theoretical predictions of the onset conditions are compared with those actually observed in standing-wave and traveling-wave engines. The results show good agreement between predictions from the model and experiments.     

Synthetical optimization of the structure dimension for the thermoacoustic regenerator

The quantitative investigation of parameters in the renegerator is essential for the optimization of thermoacoustic devices, while the majority of the previous research only considered parameters of the working field, working gas and the hydraulic radius. Based on the linear thermoacoustic theory, this paper extracts a normalized parameter for low-amplitude conditions, which is called the regenerator operation factor. By extracting the regenerator operation factor and relative hydraulic radius, the influence of frequency on the efficiency can be controlled and offset. It can be found that thermoacoustic devices with different frequencies can perform the same efficiency by adjusting the radius in proportion to the axial length. Finally, this paper synthetically optimizes the dimension of the thermoacoustic regenerator by taking the regenerator operation factor, relative hydraulic radius and acoustic field parameter as variables. Conclusions in this paper are of great significance for explaining the best working conditions of engines and directing the miniaturization and optimal design of thermoacoustic devices.     

The optimal stack spacing for thermoacoustic refrigeration

The characteristic pore dimension in the stack is an important parameter in the design of thermoacoustic refrigerators. A quantitative experimental investigation into the effect of the pore dimensions on the performance of thermoacoustic devices is reported. Parallel-plate stacks with a plate spacing varying between 0.15 and 0.7 mm are manufactured and measured. The performance measurements show that a plate spacing in the stack of 0.25 mm (2.5 deltak) is optimum for the cooling power. A spacing of 0.4 mm (4 deltak) leads to the lowest temperature. The optimum spacing for the performance is about 0.3 mm (3 deltak). It is concluded that a plate spacing in the stack of about three times the penetration depth should be optimal (3 deltak) for thermoacoustic refrigeration.     

A nonlinear model of thermoacoustic devices

This paper presents a nonlinear, time-domain model of thermoacoustic devices based on cross-sectional averaged equations. Heat transfer perpendicular to the device axis--which lies at the core of thermoacoustic effects--is modeled in a novel and more realistic way. Heat conduction in the solid surfaces surrounding the fluid medium is included. Contrary to the previous versions of this model [Watanabe et al., J. Acoust. Soc. Am. 102, 3484-3496 (1997)], the present version does not require artificial damping and is numerically robust. The model performance is illustrated on several examples: a prime mover, an externally driven thermoacoustic refrigerator, and a combined prime mover/refrigerator system.     

频率对热声制冷机影响的研究

分析和研究了频率对热声制冷机声压、温差和声功的影响 ;使用网络模型计算的结果与实验结果相吻合 ;该研究也是对网络模拟和声功测量方法的验证。     

热声发动机的格子气模拟

在传统的9-bit格子气模型中引入了温度区的概念,并应用于热声发动机的模拟研究.利用改进后的格子气模型,模拟了热声谐振管中的自激振荡和二维温度场的分布及温度随时间的演化过程,同时,对热声板叠的长度和在声场中的位置对声幅的影响也进行了数值研究,所得结果对板叠的优化设计是有价值的.通过对模拟和实验结果的比较,验证了热声机格子气模型的有效性,表明格子气方法适用于热声模拟.     

Optimal acoustic fields in compact thermoacoustic refrigerators

Thermoacoustic refrigerators have been developed during the last 15 years, employing quasi-standing resonant acoustic waves inside fluid-filled cavities to transfer heat along a stack region. Because higher efficiency can be reached when a significant travelling wave component exists in the resonator, specific resonant thermoacoustic devices have been designed allowing to adjust more or less the ratio of travelling and standing wave components. However, the acoustic pressure field and the particle velocity field do not appear to be the optimal ones, for the thermal quantities of interest. Thus, it is the aim of the paper to present a new kind of thermoacoustic standing wave-like device which allows to control easily and independently the pressure field and the particle velocity field, after investigating the optimal acoustic field, in the stack region, for the main parameters of interest, i.e. the temperature gradient, the thermoacoustic heat flow and the coefficient of performance.     

回热器的热声直流模型及其效应研究

本文由基本的守恒方程出发,获得了能描述回热器存在声直流时的非线性动力学模型及由此而导致的非线性时均热力学效应。根据所得到的模型,考察了声直流对临界声功产生率温度梯度、回热器温度分布以及脉冲管制冷性能的影响。     

Investigation of azimuthal staging concepts in annular gas turbines

In this work, the influence of azimuthal staging concepts on the thermoacoustic behavior of annular combustion chambers is assessed theoretically and numerically. Staging is a well-known and effective method to abate thermoacoustic pulsations in combustion chambers. However, in the case of, for example, fuel staging the associated inhomogeneity of equivalence ratio may result in increased levels of NO_x emissions. In order to minimize this unwanted effect a staging concept is required in which the transfer functions of the burners are changed while affecting the equivalence ratio as little as possible. In order to achieve this goal, a theoretical framework for predicting the influence of staging concepts on pulsations has been developed. Both linear and nonlinear analytical approaches are presented and it is shown that the dynamics of azimuthal modes can be described by coupled Van der Pol oscillators. A criterion based on the thermoacoustic coupling strength and on the asymmetry degree provides the modal behavior in the annular combustor, i.e. standing or traveling waves. The model predictions have been verified by numerical simulations of a heavy-duty gas turbine using an in-house thermoacoustic network-modeling tool. The interaction between the heat release of the flame and the acoustic field was modeled using measured transfer functions and source terms. These numerical simulations confirmed the original theoretical considerations.