【作者】 刘钰；

【导师】 邱利民；

【作者基本信息】 浙江大学 ， 制冷及低温工程， 2010， 硕士

【摘要】 热声发动机是一种利用热声效应进行工作的新型动力机械。整机没有机械运动部件,可采用热能驱动,常用工质为惰性气体,具有结构简单、可靠性高、环境友好等突出优点。由其驱动的制冷、发电等系统具有广阔的应用前景。回热器(或板叠)是热声发动机中实现热功转化的场所,因此提高回热器性能始终是研究者不懈追求的目标。纵观热声发展历史,每一次热声技术的飞跃都伴随着研究者对回热器不断深入的认识和革新。本文主要围绕行波和驻波热声发动机中的回热器(板叠)特性开展理论和实验研究,取得的主要进展如下：1、行波热声发动机中多段式回热器的概念以及CFD模拟优化针对现有斯特林热声发动机系统存在的回热器热损失和动力损失,结合工质物性随温度非线性变化的特点,本文提出多段式回热器的概念。采用CFD计算方法以及DeltaE软件对现有的热声斯特林发动机进行建模,模拟了以氮气为工质、充气压力为2MPa和加热器温度为766K时的压力振幅、速度振幅以及温度的系统分布。在CFD模拟中,除回热器采用层流模型外,整机采用湍流模型。通过上述两种方法得到的计算结果与实验结果对比发现：(1)CFD和DeltaE的计算结果均表明,在相同的条件下,本文提出的多段式回热发动机的性能均高于原型发动机。(2)CFD计算得到原斯特林热声热机在特定位置处(声容、谐振管入口、锥形谐振管入口)的压力振幅结果较线性热声软件DeltaE获得的结果更加接近实验值。(3)CFD计算得到起振后回热器的轴向温度呈非线性分布,DeltaE的结果为线性分布,CFD的结果与实验测量到的温度分布情况更加吻合,说明CFD方法对热声系统的温度分布具有更好的预测作用。同时,CFD计算得到多段式回热器轴向温度分布较原斯特林回热器更趋于线性分布。说明多段式回热器有助于减小回热器内部直流损失。本文还对CFD仿真得到的整机模型三通处的流场进行分析,发现该处流场由于压力和速度的剧烈变化造成一个周期内流态出现了边界层分离、漩涡等复杂流态,造成较大能量损失。这为进一步提高热声发动机性能提供了改进方向。2、驻波热声发动机丝网板叠的输出特性和起消振时序的实验研究本文利用DeltaE设计了一台小型丝网型驻波热声发动机,搭建了实验台。初步实验表明,采用丝网板叠可获得较好的性能,18目丝网时热声发动机以氮气为工质在充气压力为2.2MPa可获得0.2017MPa的压力振幅。在此基础上,开展了不同板叠参数下整机输出特性的实验研究,结果表明一定参数范围内的丝网板叠,对应的最优工作区间不同：低充气压力下,低目数的丝网对应的加热器温升速率小、加热功率范围宽,可获得最优的整机输出性能；随着充气压力的升高,高目数丝网时的加热器温升速率逐渐减小,加热功率范围变宽,可获得最优的整机输出性能。此外实验观察了各种丝网目数下驻波热声发动机起消振过程的压力与频率的时序规律,即：起振时：频率先达到本征频率,压力振幅仅有小幅上升,压力振幅在能量继续累积到一定程度时才大幅激增；消振时：压力振幅先大幅下降,然后本征频率消失。更多还原

【Abstract】 Thermoacoustic engine is a novel heat engine based on the thermoacoustic effects. It has the merits of no moving parts and can be driven by thermal energy. The working fluids are inert gases. Compared with traditional engines, it is reliable and environment-friendly. Systems driven by thermoacoustic engine have a promising future in application of refrigeration and electricity generation and so on.Regenerator (or stack) is a components of thermoacoustic engine which convert thermal energy to acoustic power. Therefore, To improve the performance of the regenerator (or stack) is the aim that researchers always pursue. Looking through the thermoacoustic history, every renovation was associated with deeper understanding on regenerator. Therefore, the following work was carried out to study characteristics of regenerator of thermoacoustic engines theoretically and experimentally.1. CFD simulation and optimization on the concept of multilayer regenerator in a Stirling thermoacoustic engineAccording to the fact that the physical properties of working fluid changes with temperature, a multilayer regenerator was proposed in a Stirling thermoacoustic engine to reduce the regenerator loss and dynamic loss. CFD tools and DeltaE were used to calculate the pressure amplitude, velocity amplitude, and temperature distributions. The working fluid is nitrogen, the filling pressure is 2MPa, and the temperature of the heater is 766K. In the CFD simulation, the whole engine uses turbulent model except that the regenerator uses laminar model. The calculation results by CFD and DeltaE were compared with the experimental results, which show: (1) Both CFD results and DeltaE results show that the engine with multilayer regenerator can obtain higher pressure amplitude than the traditional one. (2) The pressure amplitude obtained by CFD simulation agrees better with the experimental results in some specific position (compliance, entrance of the resonator) than DeltaE (3) The nonlinear axial temperature distribution is obtained after the engine onsets, while the results by DeltaE are linear. The CFD results agrees better with the experimental results than DeltaE, which indicates that CFD tools are more suitable to predict the axial temperature distribution in the regenerator of Stirling thermoacoustic engine. Besides, The CFD results shows that the axial temperature distribution is linearized in multilayer regenerator, indicating that multilayer regenerator can reduce streaming flow loss. In addition, the analysis of the flow field in the tee joint shows that the pressure and velocity change violently during an oscillation cycle. Complicated flow states such as vortex, boundary layer separation have been observed, which causes energy loss, and this result provides a further improvement direction for the engine.2. Output characteristic of the screen stack and time rule of onset and damping process in a standing-wave thermoacoustic engineA miniature standing-wave thermoacosuitc engine with screen stack was designed by DeltaE and the engine was made in the experiment. The elementary experiment shows that the engine has good performance with 18-mesh screens. With nitrogen of 2.2 MPa, the engine can produce pressure amplitude as high as 0.2017MPa The further experimental research on output characteristic with different screen stacks was conducted to optimize the screen parameters.The results illustrate the best performance of the engine depends on the screen parameters. With lower filling pressure, the screens with smaller mesh number lead to smaller increase of heater temperature and wider range of heating power, which makes the engine work with best output performance. As the filling pressure increases, the screens with larger mesh number lead to smaller increase of heater temperature and wider range of heating power. In addition, the timing rule of the onset and damping process of the thermoacoustic engine with different screen parameters were measured. In the onset process, the frequency comes to the eigenfrequency first, at the same time the pressure increases little, and then increase sharply after the energy accumulates to certain amount. In the damping process, the pressure amplitude decrease sharply first, then the frequency disappears.更多还原