Acoustic characterization of microbubble clouds by attenuation and celerity spectroscopy

Abstract

In 4th generation nuclear reactors cooled with liquid sodium, argon micro-bubbles are present in the primary opaque sodium. Acoustic control methods are chosen for operating inspections but this bubble presence greatly affects the acoustical properties of the medium. It is therefore required to characterize the micro-bubble cloud, i.e. to provide the volume fraction and the bubble size distribution. Safety authorities requires the proposed method to be robust and applicable with as few assumptions (about the bubble populations) as possible. The objective of this study is to evaluate the performance of spectroscopic methods based on celerity and attenuation in the presence of bubbles whose size and surface contributions are very different. Two methods of evaluating the histogram and the void fraction are compared. The first is based on the inversion of the integral equation of the complex wave number derived by Commander and Prosperetti[1]. The second, which assumes the populations to have log-normal or sums of Gaussian distributions, performs an adjustment of the distribution's parameters to fit spectral attenuation and celerity curves measurements. These methods are compared with experimental data obtained using ACWABUL facilities at CEA Cadarache.

Vibration of a stiffened pipe filled with a bubbly liquid: analysis of resonance frequencies in function of bubble fraction

“…It is therefore interesting to analyze the vibratory behavior of the latter in order to quantify the bubbles. Many different techniques are proposed in the literature for bubble detection or measurement: optical methods [3], acoustic methods [4], electrical or electromagnetic methods [5], methods based on the emission of ionizing radiation [6]. However, due to the opacity of sodium and the complexity of the detection environment, the acoustic methods may be the best way to detect leaks on pipes.…”