Measurement of bubble size distribution: an acoustic technique

Abstract

This paper reports the successful correlation of the bubble size distribution in a bubbly two-phase flow with the sound spectrum as measured by a hydrophone and spectrum analyser. Two types of bubbly flow were considered: (i) horizontal two-phase flow in a pipeline and (ii) a two-phase turbulent axisymmetric jet. The scientific basis of this technique of measurement lies in the well-established relationship between the bubble size and the frequency of the sound emitted by a gas bubble when it is suitably stimulated; the frequency of the sound increases as the bubble size diminishes. The development of the simple idea into a potentially useful experimental technique is discussed. The advantages of this technique, as compared to alternative methods, e.g. photographic measurements, include the suitability of the technique for use in existing opaque pipework without requiring major modifications and minimal disturbance of the flow. Results from the acoustic technique are compared with those from a photographic technique; agreement between the two methods is good. The technique was also used to predict successfully the gas-liquid mass transfer coefficient in horizontal pipelines.