热声制冷机的一种非线性模型研究

为研究热声制冷机内部的非线性过程,发展了一种可考虑管道截面积变化的时域准一维非线性热声模型,其主控方程由可压流基本控制方程经截面平均的数学处理推导得出,数值求解采用具有频散保持特性的高精度计算格式。采用该模型分别针对活塞、扬声器和热声发动机这三种不同驱动源,将驱动源和热声制冷机进行整体求解,模拟了热声制冷板叠两端温度差在气体微团吸放热的循环过程中逐渐增大的整个过程,预测了谐振管内部驻波的非线性畸变。进而研究了平均工作压力、板叠材料、板叠位置以及扬声器形状等参数的选取对于热声制冷机制冷效果的影响。     

非平行板叠驻波型热声发动机热力性能研究

热声发动机板叠两端存在较大的温度梯度,导致沿板叠轴向的热渗透深度出现严重的不均一性,影响到热声转换效应的发挥。本文提出了板叠结构形式与温度梯度相一致的结构设计理念,并构建了非平行板叠结构的驻波型热声发动机数理模型。针对不同板叠锥角热声发动机的热力性能展开了深入研究和对比分析,得出板叠锥角对热声发动机频率、压比、压力振幅和体积流率等热力参数的影响关系。结果表明:与平行板叠结构相比,当选取合适锥角时,渐缩和渐扩式板叠结构均可提高热声系统的性能,在1°和-2.81°时系统的最大声功流分别提高了103.9%和88.8%。研究结果为进一步改善热声热机性能提供理论支撑。     

黎开管非线热声效应的研究

基于能量守恒原理对Rijke管热声效应展开了理论分析,采用内外流场耦合法数值模拟了Rijke管自激励起振和饱和过程的声场特性,并开展了相应的实验研究.推导了Rijke管起振、饱和及高次谐波产生过程中的能量变化,分析了Rijke管非线性效应包括高次谐波和波形畸变的影响因素,提出了改变管口声阻抗可弱化非线性效应的方法.结果...     

热声制冷机板叠内流动与换热的数值分析

本文采用基于压力修正算法的可压缩交变流动程序,采用适体坐标生成网格,AUSM 格式离散N-S方程和能量方程,计算了二维基本型热声制冷机板叠内的流动与换热情况,探讨了板叠附近的温度随时间的变化,分析了周期时均能量.由模拟结果可以看出,在气体冷端,能量由气体进入板叠,时均能量为正,在气体热端,能量由板叠进入气体,时均能量为负,板叠热端的时均能量稍大于板叠冷端的时均能量,板叠产生了冷量.但与输入功相比,板叠产生的冷量较小,因此系统的内能增加,气体冷端的温度增加.并且随着板叠的厚度的增加,板叠冷热端温差先增大后减小,并存在最佳板叠厚度使得冷热端的温差达到最大.     

Rijke热声振荡的非线性效应

本文研究了Rjike管热声振荡的非线性效应，指出了引起非线性效应的两个因素，即热声相互作用的非线性和声波在管子末端的非线性辐射声阻,并通过计算声波振幅的增长率和实验分析声波的频谱，发现非线性效应限制了管内声波振幅的增长，并且导致了二次及高阶谐波的产生。     

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。     

热声现象的一种非线性模型的研究

本文对一种准一维非线性热声模型进行研究,利用该模型初步预测了一种热声驱动器的工作特性,并采用一种更简便的差分格式对系统中发生的非线性现象进行了数值模拟。结果表明,在频域内和线性条件下,该模型简化为经典的线性热声模型,可以预测热声驱动器的起振温度梯度;在时域内和非线性条件下,该模型可以模拟热声系统内的瞬态压力波由初始增长,经过非线性演化,最终达到饱和的全过程;最后,还讨论了板叠上的温度差对饱和压力波的影响。     

强激光场中N2分子高次谐波的干涉效应

在强场近似下,利用Lewenstein模型研究了N2分子在强激光场中发射高次谐波的干涉效应,通过对N2分子产生的高次谐波和分子中单个原子产生高次谐波的比较,表明了干涉效应的存在. 得出随着高次谐波阶数的增加,干涉极小值会随着分子轴与激光偏振方向间夹角的增加而减小,在角度接近900附近时干涉效应消失,与两中心干涉模型预测的趋势一致. 通过分析高次谐波产生的机制和相位随取向角的变化,给出了干涉产生的原因.     

驻波热声冷却机的研究

与压缩机制冷相比,热声制冷结构简单、可靠性高和使用寿命长。本文在正常室温(20℃)和室压(1个大气压)的工作环境下以空气为声学介质来探讨热声制冷机的设计及热声制冷效果的影响因素,并制作样机进行实验研究。研究发现:板叠长度和中心位置对热声转换效率影响较大,其数值需要理论与实验相结合来确定;以空气为声学工质,在正常室温、室压下的热声制冷机,用50W的供电驱动、90 Hz工作时可实现冷热端37℃的温差。     

扬声器驱动热声制冷机的研究进展

热声制冷技术是一项新型的制冷技术,它具有运动部件少、运行可靠、振动小、寿命长、对环境无污染等优点,在航天、超导、低温电子、低温生物等众多领域有着十分广阔的应用前景。本文阐述热声制冷效应的基本原理和热声制冷循环之后,系统介绍了热声制冷机中共振管、板毪、换热器、动力源(扬声器)等部件和制冷工质的研究情况。同时,指出了扬声器驱动热声制冷存在的问题,并对热声制冷的发展进行了展望。     

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.     

扬声器驱动热声制冷机设计研究

热声制冷机主要由声驱动器、共振管、板叠、高低温端换热器、声容等部件组成。它具有运动部件少、运行可靠、振动小和寿命长等优点 ,在军事、航天、微电子、低温物理等领域有着十分诱人的应用前景。文中运用经典线性热声理论对热声制冷机各个组成部件设计进行了介绍 ,在此基础上设计了一台扬声器驱动热声制冷机 ,并用专业计算软件进行了数值模拟验证 ,为热声制冷机进一步优化与发展提供了一个解决方案。     

Nonlinear impedances of thermoacoustic stacks with ordered and disordered structures

Nonlinear impedances of two thermoacoustic stacks with ordered structures （plate-type and pipe-type） and one with a disordered structure （copper mesh） are studied. The linear resistances, nonlinear coefficients and effective acoustic masses of the stacks are extracted from the experimental results based on an analogical model of nonlinear impedances of porous materials. The resistance and nonlinear coefficient of the disordered stack are found to be much larger than those of the ordered stacks, which have similar volume porosities. In the ordered stacks, the resistance is only marginally influenced by the length of the stack, while in the disordered stack, the resistance increases significantly with the length. These charac- teristics of the impedances of ordered and disordered stacks are explained with the minor loss theory and the tortuosity of a stack.     

热声热机中的能量模拟与分析

文中主要对回热器中的能流及其能流分量进行了模拟 ,并在此基础上分析了能流及其分量对热声热机的影响 ,为更深地理解热声热机中所发生的能量转换现象 ,更好地设计热声热机提供有价值的依据和参考。     

Parallel capillary-tube-based extension of thermoacoustic theory for random porous media

Thermoacoustic theory is extended to stacks made of random bulk media. Characteristics of the porous stack such as the tortuosity and dynamic shape factors are introduced into the thermoacoustic wave equation in the low reduced frequency approximation. Basic thermoacoustic equations for a bulk porous medium are formulated analogously to the equations for a single pore. Use of different dynamic shape factors for the viscous and thermal effects is adopted and scaling using the dynamic shape factors and tortuosity is demonstrated. Comparisons of the calculated and experimentally derived thermoacoustic properties of reticulated vitreous carbon and aluminum foam show good agreement. A consistent mathematical model of sound propagation in a random porous medium with an imposed temperature is developed. This treatment leads to an expression for the coefficient of the temperature gradient in terms of scaled cylindrical thermoviscous functions.     

热声发动机用加热器的设计与实验验证

热声发动机利用热声效应将热能转换为机械能,热能由核心部件加热器提供。加热器在热声发动机的能量传递和转化过程中起着举足轻重的作用。针对热声发动机的工作特点,介绍了一种采用时均流对流换热公式进行热声发动机用加热器设计的方法。基于该方法,设计了一种新型热声发动机用电加热器,并应用于自行研制的太型多功能行波热声发动机试验台。设计计算和实验结果表明,该加热器能够充分满足热声发动机的加热要求。本文对以振荡流体为特征的换热器设计具有一定参考价值。     

Acoustic coupling between the loudspeaker and the resonator in a standing-wave thermoacoustic device

Thermoacoustic refrigerators work with high amplitude sound waves, which are often created using an acoustic source coupled to a resonator. This coupling can be calculated analytically using linear acoustic equations and a linear model of the loudspeaker. This paper makes a comparison between such a coupling and measurements obtained in a large-scale thermoacoustic resonator constructed at the University of Manchester. The resonator was driven from low to large pressure amplitudes, with drive ratios up to 10%. It is shown that a good agreement is obtained for small amplitudes and this progressively worsens as the amplitude is increased. In the absence of wave harmonics and loudspeaker nonlinearities, the increasing discrepancy is attributed to the presence of minor losses.     

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.     

The experimental studies of thermoacoustic cooler

The experimental studies of thermoacoustic cooler consisting of acoustic loop-tube were carried out. The loop-tube was filled with the mixture of air and helium gas or air at atmospheric pressure. The dimensions of the loop-tube were 3.3 m of length, 44 mm of inner diameter and 4 mm of thickness. A pair of stacks (stack 1 and stack 2) which were sandwiched between two heat exchangers was placed symmetrically in the loop-tube. Stack 1 was employed as a prime mover and stack 2 as a heat pump. The self-sustained sound generated by the thermoacoustic effect and the cooling phenomena at the stack 2 were observed. The distribution of the sound pressures and the waveforms in the loop-tube were measured, and the frequency component of the self-sustained sound was investigated at the starting phase. The fundamental frequency component was confirmed and it was developing as the sound pressure increasing. The higher harmonics frequency components were generated and they were also developing.