Acoustical characterisation and monitoring of microbubble clouds

Abstract

Argon microbubbles will exist in the primary sodium of the next generation of sodium-cooled fast reactors (SFR). Due to its opacity, acoustic methods will be used for the in-service inspection in these reactors, but the presence of such bubbles will greatly affect ultrasonic wave propagation. Moreover, these bubbles can lead to the formation of gas pockets in the reactor and impact cavitation and boiling phenomena. It is therefore necessary to characterise what is called the 'microbubble cloud' by providing the volume fraction and the bubble size distribution. Safety requirements in this field call for robust inspection methods based on very few assumptions about the bubble populations. The objective of this study is to assess the performance of spectroscopic methods in the presence of bubbles with high polydispersity and to monitor an evolving cloud of microbubbles. The histogram and void fractions were estimated according to the regularised inversion of the complex wave number's integral equation. To reduce the need for prior information on the bubble cloud, a specific procedure was used to estimate the maximum radius of the population. The results are presented on the basis of the experimental data obtained and then compared with optical measurements.

Numerical Characterization of Acoustic Cavitation Bubbles with Respect to the Bubble Size Distribution at Equilibrium

“…Let us consider a log-normal distribution [27,56,57] of the number density of bubbles according to their ambient radii, with an expected value of 3 µm, fairly acceptable as the average equilibrium radius at 300 kHz frequency [29]. The following notation is then adopted.…”

“…On the other hand, literature counts several studies that attempted to characterize experimentally multibubble populations. For instance, D'Hondt et al [27] used spectroscopic techniques to characterize the microbubbles cloud by providing the gas volume fraction and the bubble size distribution. The authors suggested a procedure based on L-Surface analysis and applied to log-normal size distribution of bubbles in water.…”

Rheological investigation of bitumen, used for radioactive waste conditioning, with ultrasonic waves

“…In the context of assessing opaque materials, ultrasonic approaches emerge as particularly relevant. The detection of ultrasonic bubbles has been widely discussed in the scientific literature [16][17][18][19][20][21], catering to the needs of diverse industries. These methods are used particularly in high-speed fluidics (cavitation problems), in agronomy for pasta development [16] or emulsion control [17], as well as in the polymer industry (foams in the broadest sense).…”

Theoretical and Experimental Studies of Acoustic Reflection of Bubbly Liquid in Multilayer Media

“…Vanhille et al [22][23][24] numerically simulated the propagation of acoustic waves in bubbly liquids and analyzed their nonlinear characteristics. Cavaro et al [25,26] experimentally analyzed the acoustical characterization of microbubble clouds.…”