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。     

热声热机结构动力学分析

利用商业软件ANSYS建立热声热机模型,从结构动力学角度进行模拟研究,对其进行结构静力、模态和谐响应分析。在热声系统的关键位置布置监测点,得到热声系统内部位移、应力和应变等参数随压力和频率的变化关系。研究结果表明:随着充气压力的提升,应力应变基本呈现线性增大的趋势,且峰值点一一对应。随着结构模态的提高,热声热机的应力和应变因位置的不同而存在差异;热声系统的3阶和4阶模态下固有频率接近气体介质的振荡频率;由谐振管内表面布置的监测点所得结果可知,高密度的气体介质的振荡会在回热器中产生振动激励和声激励,并作用于谐振管,使声波和固体介质产生共振和耦合。     

高频驻波热声热机的数值研究

以1/4波长驻波热声热机为研究对象,建立了平行板叠结构回热器以及异形板叠结构回热器的数值模型,采用Fluent软件分析了这两种结构回热器产生的压力、速度以及流场.研究结果表明:异形板叠结构回热器自激振荡达到饱和所需的时间比较短,压力幅值比较高;非线性声场的扰动,导致不同时刻回热器冷热两端温度分布不稳定,相比平行板叠结构回热器,异形板叠结构回热器温度梯度比较小,有利于低品质热源的应用;针对板叠结构回热器,改变平板的结构,有利于实现热声系统的匹配;异形板叠结构回热器周围的流场明显强于平行板叠结构回热器,有利于流固之间的耦合,提高了热声转换的效率.     

双驱动热声热机谐振管中声波的传播特性研究

分析了双驱动热声热机谐振管中声波的传播特性,通过分析指出,对于双驱动的热声热机,可以通过改变其反射系数和驱动声源的驱动相位差,进而实现谐振管声场的声压幅值和声场相位的改变.理论研究表明,在|rp|=0.3,相位差为σπ=0.5π时的声压幅值大于σπ=π的声压幅值;而在σπ=0.5π时,声场幅值随反射系数|rp|的增大而增大.实验研究表明,在相位差σπ为常数时,通过改变不同的反射系数值,就可以实现谐振管中声场的调节;在反射系数|rp|为常数时,通过改变谐振管两边驱动声源的驱动电压值,也可以实现声场幅值和相位差的调节.这样就有利于调节结构已经确定的微型热声热机的最佳声场分布,使其达到最优热声转换效率,实现微型双驱动热声制冷机热声制冷效率的最优化.     

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.     

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。     

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。     

正弦振荡器起振条件的定量分析

正弦振荡器在晶体管和电路参数确定后，只能在一个频率上产生正弦振荡。振荡稳定后，要满足振荡平衡条件；但在接通电源后要建立起稳定的正弦振荡，电路又必须满足起振条件。本文从分析AF＞1这个起振条件入手，依据相位平衡条件φA φF=2nπ，求得振荡频率f0；依据│AF│＞1，求满足起振条件时所需的晶体管及电路参数值。并对一个具体振荡电路进行了定量分析。     

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.     

Advances in thermoacoustic engine and its application to pulse tube refrigeration

Thermoacoustically driven pulse tube refrigerator, a novel cryocooler without any moving components using heat energy as driving power, attracts much effortsfrom the researchers in the field of cryogenics and refrigeration in the past decades. After a short introduction of the history about thermoacoustics, we presented the key technology, followed by a detailed review on theoretical and experimental developments and advances of thermoacoustics.The prospective research emphases are also presented at the end of this review.     

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.     

3kHz微型驻波热声发动机的实验研究

以芯片冷却为应用背景,在线性热声学理论的指导下,以降低起振温度、获得较高的热声转换效率为目标,进行了机型的选择和热声热机核心段的设计.研制了一台3.3kHz微型驻波热声发动机,长度为55mm,由加热器、回热器、冷却器及谐振管4部分组成.在9W的加热量下,热端温度78℃时该发动机产生自激振荡,起振温差为26℃.稳定运行后...     

车用汽油机过渡工况进气管内油膜动态特性建模及仿真

分析了汽油机过渡工况时Aquino油膜模型的动态特性。提出了一种考虑进气状态参数的进气管内油膜特性动态模型．以汽油机两种过渡工况为例,利用Simulink分别对基于Aquino模型和动态模型的汽油机空燃比变化进行了仿真,并与汽油机试验数据进行对比．研究结果表明,提出的动态油膜模型能较准确地描述过渡工况进气管内燃油动态特性,其精度优于Aquino模型．     

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.     

A high pressure-ratio, energyfocused thermoacoustic heat engine with a tapered resonator

Heat energy with temperature difference may lead to self-excited acoustical oscillation under appropriate condition, which is called “thermoacoustic phenomenon”. The physical phenomenon was observed about two hundreds years ago. However, the research on high-energy thermoacoustic devices was begun only about a decade ago.Thermoacoustic machines use inert gases as working medium and have no moving mechanical pans; consequently they are really environment-friendly and highly reliable.The efficiencies of thermoacoustic machines are now greatly improved, close or even higher than that of conventional heat engines.