In situ ultrafast synchrotron x-ray imaging studies of the dynamics of ultrasonic bubbles in liquids

Tan, Dongyue

Abstract

The research studies the highly dynamic and transient behaviour of ultrasonic bubbles in liquids of different physical properties, including water, silicone oil, and liquid metals. A novel ultrasound solidification apparatus as well as the special sample containers and the relevant control systems were designed, built and commissioned for this research.

Systematic in situ experiments were conducted using this novel apparatus at the ultrafast synchrotron X-ray imaging (271,554 fps) beamline, the sector 32-ID-B of Advanced Photon Source (APS) and the high speed X-ray imaging beamline, I12 of Diamond Light Source (DLS) in 2011-2015.

A huge amount of real-time images were obtained in this research, a procedure and the relevant in-house Matlab code were developed to analyse those images and extract the key information for understanding the highly dynamic behaviour of the nucleation, oscillation, implosion, coalescence of ultrasonic bubbles and bubble cloud. The ultrasound induced acoustic flows coupled with bubbles and particles were also investigated, and their effects on liquid-solid interface during the solidification of a Bi-8%Zn were analysed and quantified.

The experiments were complemented by the modelling and simulations of the acoustic pressure field, the bubble dynamics using the classical Helmholtz Equation and Gilmore model, providing more quantitative understanding for the interactions of ultrasonic waves and bubbles with the liquids and the solid phases in the liquids.

The key research findings are:
 For bubble implosion: For the first time, bubble implosion in liquid metal was captured in real-time and in situ. In both water and liquid Bi-8%Zn, compressed gas cores were found at the centre of the imploding bubble with shock waves emitted outwards from the centre.
 For bubble oscillations at quasi-steady state condition, the measured bubble radii agree well with the predictions made by Gilmore model for all liquids studied in this research.
 For bubble coalescence, the time needed for liquid Bi-8%Zn cannot be predicted using either the no-slip or the free interface model. A new power law model is developed and the prediction made using this new model agrees well with the experiments.
 For the first time, in metal alloys, the in situ and real-time studies proved that the ultrasonic bubbles and the acoustic flows are capable of fracturing and detaching the solid phases from the liquid-solid interface.
 Temperature fluctuations caused by applying ultrasound in Bi-8%Zn during solidification is capable of detaching the solid phases from the liquid-solid interface. However, it is less important and slower than acoustic flows and ultrasonic bubbles.
 Ultrasound power is a dominant parameter for the interactions of ultrasonic bubbles, acoustic flows, temperature fluctuations with liquid-solid interface.

Citation

Tan, D. In situ ultrafast synchrotron x-ray imaging studies of the dynamics of ultrasonic bubbles in liquids. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4217504

• Thesis Type: Thesis
• Deposit Date: Dec 18, 2015
• Publicly Available Date: Feb 23, 2023
• Keywords: Engineering
• Public URL: https://hull-repository.worktribe.com/output/4217504
• Additional Information: School of Engineering, The University of Hull
• Award Date: Aug 1, 2015