喷嘴释放单气泡的声发射特性

利用声发射技术在单气泡发生实验装置中研究了气液两相流中单气泡的动力学特性，使用自行开发的采集处理程序进行气泡声信号的参数提取，采用统计分析、小波变换和快速傅里叶变换对声信号进行时域和频域范围的分析。分析结果表明，声发射技术可以检测到管内气泡的声信号，具有较高的信噪比，且声信号随着喷嘴尺寸的增大而增大，随着液相表面张力的减小而减小。比较不同喷嘴直径下气泡的频率谱，发现喷嘴释放气泡发出的声信号频率为150～200 kHz，且随着喷嘴直径的增大，峰值频率相应增大，提出了声信号峰值频率与气泡尺寸之间的关联式。同时得到了气泡上升过程中的连续形态变化，分析了气泡产生声音的机理。研究表明，声发射技术是一种灵敏度高、测量手段方便的方法，可用于气液两相流气泡运动特性的检测。

Acoustic emission characteristics of single nozzled bubble

Dynamic characteristics of single bubbles in gas-liquid two-phase flow were studied by acoustic emission technique in an experimental setup of single bubble generator. Parameters of acoustic emission signal in bubbles were extracted using self-developed data acquisition and processing program. The acoustic signals in time and frequency domains were then analyzed by statistical analysis, wavelet transform and fast Fourier transform. The results showed that the acoustic emission technique could detect acoustic signals of bubbles inside tube with a high signal to noise ratio, which the acoustic signal increased with the size of nozzle but decreased with the surface tension of liquid. By comparing frequency spectra of bubbles from nozzle with different diameters, it was found that the acoustic signal frequency emitted by bubbles was between 150—200 kHz and peak frequency increased with nozzle diameter. A correlation function was proposed between peak frequency of acoustic signals and bubble diameter. Meanwhile, a continuous bubble evolution diagram was obtained for bubble floating up and generation mechanism of acoustic signals by bubbles was analyzed. The study demonstrates that acoustic emission technique is highly sensitive and very convenient for measurement of bubble motions in gas-liquid two-phase pipe flow.