多孔填料回热器工质的压缩性研究

讨论了微型热声热机中气体工质在非等截面的多孔填料回热器中的压缩性,指出表征热声热机热声效应的热函数和粘性函数以及由热声效应所产生的平均功流均与工质在多孔填料中的压缩性虚部相关.理论研究表明,通过改变填料的特征尺寸就可以达到改变工质压缩性虚部的目的,进而可以获得最大的热声效应所产生的功流.     

多级环形热声热机的起振条件及特性

基于线性热声网络理论,推导了多级环形行波热声热机的起振条件式,并对无负载系统的起振及稳态特性进行数值模拟分析.重点研究了不同工质、充气压力、回热器丝网水力半径及热声芯级数对热声热机起振温度、自激振荡频率以及相应声功率和效率的影响.模拟结果表明:不同充气压力下均存在获得最低起振温差的最优丝网水力半径,且在最优值附近存在一个合适的选值范围,使起振温差随充气压力的增加而降低,充气压力对振荡频率的影响不大;起振温差和振荡频率均随热声热机级数的增加而减小,当回热器温差一定时,增加级数会降低单个热声芯产生的声功率和效率.在一定加热功率条件下,采用混合工质可以获得比氦气工质更低的起振温差,且能获得与氦气工质相当的高声功率,因此混合工质有利于降低热机系统的工作温度和低品位热能的利用.     

热声热机板叠式回热器结构数值计算

将热声热机板叠式回热器气体通道看成矩形导管,对回热器结构进行数值计算。通过声波导管理论的推导,对微型热声热机回热器板叠尺寸进行研究,利用高次波在气体通道衰减原理,计算回热器板叠纵向长度。研究结果表明:50kHz的热声热机回热器板叠最小横向长度为3.43mm;横向长度为3.43mm的板叠对于频率分别为20,30,40kHz的3种声源的最佳纵向长度分别为5.9,6.0和6.4mm,最佳纵向长度随声源频率的降低而减小。     

热声热机中回热器的数值计算与分析

针对热声热机系统回热器（或板叠）的数值计算。讨论了简单实用的得谐分析方法,并对热声制冷机中的热声板叠进行了数值计算与分析。计算结果为回热器（或板叠）的设计与优化奠定基础,从而保证系统设计的可靠性。     

热声热机——无运动部件的低污染热机

通过对国内外热声热机理论和实验研究的分析，展望我国发展热声热机的前景。     

二热源热机的统一描述

应用有限时间热力学理论,对一类二热源热机作了统一的描述,导出以理想气体为工质的二热源热机的输出功率与效率间的优化关系,并讨论了回热损失和回热时间对输出功率和效率的影响．所得结果具有普遍意义,可为斯特林热机、埃里克森热机等一类二热源机的优化设计和最佳工作参数的选择提供些新理论指导     

实际热声热机微热力学循环性能优化

分析实际热声热机微热力学循环中的诸多因素,运用有限时间热力学方法,导出实际热声热机微热力学循环的效率与输出声功率的最优关系,分析不可逆程度因子及热漏系数对此最优关系的影响.结果表明:实际热声热机微热力学循环中存在一最佳温度振荡值,使循环在得到高效率的同时得到高输出功率,并由数值计算认证了这一结论.     

无温度梯度条件下高频热声核的特征阻抗和传播常数实验辨识

从热声学研究角度对丝网堆积型热声核的特征阻抗和声传播常数进行了实验辨识.首先描述了作为热声热机中第二热力学介质的多孔材料-热声核的特征阻抗和声传播常数的实验辨识方法.由于基于波动理论的双传感器声场重构方法的提出,使得热声核前后表面的声阻抗率的实验确定成为可能,因此热声核的特征阻抗和声传播常数的测量不再要求热声核后必须为特殊的声场条件(刚性盖板或四分之-波长空气层厚度),可以为任意声场条件,这一改善使得作为热声热机的核心元件的热声核所需要的热声学边界条件得以满足.实验辨识结果给出了无温度梯度下,高频声场中所测频段内被测热声核的特征阻抗和声传播常数.其值与热声热机中所观察到的现象相符.     

线性唯象传热定律下具有非均匀工质的一类非回热不可逆热机最大功率输出

我们对具有非均匀工质的一类非回热不可逆热机的最大功率输出进行了研究,考虑工质与热源间传热服从线性唯象传热定律[q∝Δ（T^-1）],利用最优控制理论分别导出了集总参数模型和分布式参数模型下热机的最大功率．研究结果表明分布式参数模型下的热机最大输出功率要小于或等于集总参数模型下的热机最大输出功率,且对实际热机更具有指导意义．对恒温热源下工作的不可逆热机特例,给出了其最大功率的解析表达式．采用数值计算方法给出了变温热源下的集总参数模型算例,分析了热源温度变化对热机最大功率的影响,并与牛顿传热定律[q∝Δ（T）]下的相应研究结果进行了比较．     

异型回热器热声热机结构动力学分析

利用商业软件ANSYS从结构动力学角度模拟分析了回热器结构的改变对热声热机的影响.在之前研究的基础上,改造了普通板叠回热器的结构,建立针束、肋片板、微坑板异形回热器模型,对包含各回热器的热声整机模型进行了结构动力学分析.分析得出,普通板叠回热器热声热机在150Hz附近谐振,而异型板叠回热器热机由于结构的改变,共振频率发生变化,在高阶模态应变到达峰值,说明了回热器的结构优化是提高热声热机性能的有效手段.     

Two-port network model and startup criteria for thermoacoustic oscillators

The startup process of a thermoacoustic engine is a self-excited oscillation process generated in inhomogeneous acoustic media. To reveal these coupling relations between various influential factors is an important task of basic research on thermoacoustics. In this paper thermoacoustic engines are regarded as thermoacoustic oscillators consisting of the active network and the passive network. Accordingly, the two-port Y-parameter for relevant component is derived, and standing wave and traveling wave thermoacoustic engine are described by the negative-resistance and feedback model, respectively. The relevant two-port network topology is given as well. The startup criteria for thermoacoustic oscillators are obtained by using Nyquist instability criterion. The model prediction of startup parameters, particularly, startup frequency and mode characteristic are in agreement with that of experimental results reported in the literature. Moreover, with topological graphs it is verified that standing wave engines would start up in a negative-resistance state and there would exist high frequency modes in thermoacoustic-Stirling engines. By investigating into the frequency response of thermoacoustic system, this method proposed can achieve such an objective that these effects of operating and structural parameters of engine on startup modes and startup temperature can be revealed in an analytical way. Thus this approach to test and check thermal stability can be provided in a design phase, instead of using empirical frequency to design thermoacoustic systems. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. Supported by National Natural Science Foundation of China (Grant Nos. 50576024 and 51076013)     

Characteristics of onset and damping in a standing-wave thermoacoustic engine driven by liquid nitrogen

We explore characteristics of onset and damping in a thermoacoustic engine (TE) driven by cryogens instead of conventional heat sources above the ambient temperature by a comprehensive study of a self-made standing-wave thermoacoustic engine driven by liquid nitrogen. The experiments verify the feasibility of enhancing the thermoacoustic oscillation at cryogenic temperatures. The onset temperature difference along the stack of the TE significantly decreases, compared with that of a conventional TE driven by high-temperature heat sources. The resonance frequency of the cryogen-driven TE is smaller than that of the heat-source-driven TE, mainly due to the lower average temperature of the working gas. Experiments and calculations show that the temperature discrepancy between onset and damping is partly caused by the linear temperature distribution along the stack before damping, together with the nonlinear distribution before onset. These results will contribute to a better understanding of thermoacoustic oscillation and to the recovery of the cold energy of cryogens.     

通过柴油机性能参数确定示功图方法的研究

提出一种利用柴油机性能参数，如柴油机功率，爆发压力等，计算其示功图以及放热率的新方法，该方法是利用双韦贝函数替代柴油机放热规律，以模拟计算出的爆发压力和功率与实测值最接近为目标函数最优选取双韦贝函数中的五个常数，然后利用优选出的结果进行柴油机工程过程计算，从而得出示功图，算例分析表明，采用上述方法计算出的示功图与实测示范图吻合。     

热声发动机回热器操作因子的优化研究

研究热声热机中回热器长度和工作温度的优化方法.通过对热声学线性公式的进一步分解,提炼出一个量纲一参数———回热器操作因子.相对水力半径和回热器操作因子建立了工作频率与回热器长度及回热器水力半径之间的定量关系.通过回热器轴向尺寸和径向尺寸的一定比例缩放,使得热声系统在不同频率下实现相同的热声转换效率.以两种典型的热声发动机回热器为例,对操作因子进行优化研究,并由此得到了最佳工作效率下的回热器长度和温度分布.     

Influence of resonator diameter on a miniature thermoacoustic Stirling heat engine

A small scale thermoacoustic Stirling engine （TASHE） is simulated according to the linear thermoacoustic theory. The computed results show that in a small scale thermoacoustic Stirling heat engine, the diameter of the resonance tube might have important influences on the working frequency and the performance of the engine, which are always neglected in a large scale system. Likewise, the analysis and experimental results show that in order to obtain better engine performance, the diameter of the resonance tube must be chosen appropriately according to the looped tube dimension and the input heating power. This provides an effective way to miniaturize the thermoacoustic Stirling heat engine. According to the computation and analysis, a small scale engine was built, the resonance tube length and diameter of which were about 350 mm and 20 mm, respectively, and the working frequency was about 282 Hz. When the input heating power was about 637 W, the maximal peak to peak pressure amplitude and pressure ratio reached 0.22 MPa and 1.116, respectively, which were able to drive a thermoacoustic refrigerator or an electrical generator.     

车用发动机进气过程和进气均匀性的数值计算

利用所建立的换气模型和特征线方法对车用发动机的进气过程和进气均匀性进行了数值计算和分析，研究结果表明，所采用的计算方法和计算程序具有较高的实用价值．研究方法为改善车用发动机缸内燃烧过程的均匀性提供了有效的研究手段．     

多缸汽油机充气效率和进气均匀性研究

利用所建立的进气模型,对多缸汽油机的进气特性进行了数值计算和分析,结果表明所采用的计算方法和计算程序具有较高的精度。文中还对多缸汽油机的进气不均匀性和不均匀偏差作了研究。     

热声热机谐振管截止频率选择机理

通过波导管理论的推导，对热声热机中谐振管的截止频率选择机理进行研究，导出谐振管中传播一维平面波的频率传播范围，阐述热声热机谐振管中一维平面波的传播机理，即谐振管截止频率选择的理论依据。理论研究结果表明：对于同样等效直径的矩形谐振管，其截止频率远大于圆形谐振波导管的截止频率；对于等效半径为2mm的微型热声制冷机的谐振管，当声速为343m／s时，谐振管的截止频率为50248Hz，实际的工作频率5500Hz，远小于谐振管的截止频率；在热声热机谐振波导管中只存在一维平面波传播，有利于合理布置热声热机的其他部件，达到优化热声热机的目的。     

A high-performance thermoacoustic refrigerator operating in room-temperature range

The working principle of an efficient travelling- wave thermoacoustic refrigerator operating in room-temperature range has been analyzed and an experimental set-up has been built. The experiment showed that suppressing DC-flow streaming was very critical to efficient operation, and an elastic membrane was used to solve the problem successfully. At the most efficient operating point, the novel thermoacoustic refrigerator achieved a cooling capacity of about 80 W at -20℃, with a much higher efficiency than previously developed standing-wave thermoacoustic refrigerator.