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.