MICRO-HEAT TRANSFER MECHANISM IN A BOUNDARY LAYER INDUCED BY ACOUSTIC OSCILLATION AND THE DEVELOPMENT OF THERMOACOUSTIC THEORY

众所周知，边界层是由正弦振荡形成的。这种边界层的厚度(称为穿透深度)和那里的热流行为控制着声谐振管制冷机的系统性能。在理论和数值分析的基础上，导出了这种换热的标度参数：普朗特数、振荡雷诺数、斯特罗哈尔数与流体振动幅度和堆叠距离的关系、斯特罗哈尔数与堆叠长度和堆叠长度的关系以及堆栈与流体的热容比。将堆叠温度分布的实验数据与线性化热声理论进行了比较，结果表明斯特罗哈尔数具有重要的意义。与斯特罗哈尔有关的重要因素之一。数值是由于流体粘性的存在而引起的声学流动。然后进行了流可视化研究，以深入了解堆栈对流的影响。声学流动呈现出在堆叠两侧出现两个旋涡的特征，并且这两个旋涡之间通过贯通流动相互结合。这表明在发展预报模型时考虑这种旋涡和贯通流动是很重要的。另一种改善性能的方法是控制速度和压力波动之间的相位差，和/或控制堆叠两端的速度。其中一种典型的技术是在声学驱动器和共振管的封闭端之间安装旁路。然后，带有共振盒的旁路已经显示出提高性能的潜力。

It is well known that the boundary layer is formed by a sinusoidal oscillation. The thickness of this boundary layer (referred to as the depth of penetration) and thermal flow behavior there control the system performance of acoustic resonance-tube refrigerator. The scaling parameters of such heat transfer are derived based on the theoretical and numerical analysis as follows : the Prandtl number, the oscillation Reynolds number, the Strohal number with respect to the amplitude of fluid oscillation and the stack distance, the Strohal number with respect to the amplitude and the stack length and the heat capacity ratio of the stack and the fluid. Comparison between the experimental data of temperature distribution along the stack and the linearized thermoacoustic theory indicated a prime importance of the Strohal number. One of the important factors related to the Strohal. number is an acoustic streaming induced by the existence of fluid viscosity. Then the flow visualizing study was conducted to look insight into the influence of the stack on the streaming. The acoustic streaming showed characteristic feature that two vortices appeared at both sides of the stack and moreover that these two vortices were combined with each other by the through flow between them. This suggested the importance to take such vortices and through flow into account in the development of prediction model. Alternative approach to improve the performance is the control of the phase difference between the velocity and pressure fluctuation, and/or veloci es at both ends of the stack. One of the typical techniques is to install the by-pass between the acoustic driver and the closed end of the resonance tube. Then the by-pass with a resonance box has shown the potential to improve the performance.