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Hunter-Brown, George (2023) Diamagnetic Levitation of Bubbles and Droplets. PhD thesis, University of Nottingham.

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Abstract

This thesis describes the use of diamagnetic levitation to study fluids in a zero-gravity environment, particularly focusing on bubbles and droplets. We use a strong nonhomogeneous magnetic field (maximum field strength 18.5~T) generated by a superconducting solenoid magnet to repel/attract materials at a molecular level allowing for a net zero body force to be experienced by bubbles/droplets.

A new technique that allows for the suspension of spherical gas bubbles in liquids at room temperature is presented. The development of this technique allowed for several novel experiments to be carried out.

Firstly, we use this technique to observe the coalescence of multiple pairs of air bubbles in water, starting from hydrostatic equilibrium. The coalescence creates large axisymmetric perturbations to the surface of the bubble which leads to the ejection of satellite bubbles. For the first time, we experimentally observe the simultaneous ejection of two satellite bubbles from the coalescence of a pair of air bubbles.

After satellite bubbles are ejected, the bubble formed from the coalescence of the parent bubbles undergoes large nonlinear axisymmetric surface oscillations. We analyse these surface oscillations for two cases: a symmetric case, where the initial parent bubbles have equal radii (within experimental error) and an asymmetric case where the ratio of the radii of the two parent bubbles is $\sim1.5$. We compare our results to the analytical model of Tsamopoulos and Brown and find that in the symmetric case, when only a single large amplitude surface mode is dominant, that experiment and simulation agree well with theory and the oscillation frequency of the dominant mode behaves as a function of the square of its amplitude. But, in the case several surface modes are oscillating with moderate or large amplitudes, agreement between the model of Tsamopoulos and Brown and what is observed in experiment and simulation is seen to be less accurate.

Secondly, we use this technique to observe and manipulate bubble clusters. We show that if a small amount of surfactant is added to the liquid, that air bubbles levitating in the liquid may remain in contact with each other without coalescing for an indefinite period of time. This allows for the creation of clusters of multiple diamagnetically levitated spherical air bubbles. We present bubble clusters created from up to 21 bubbles and show how the arrangement of these clusters may be altered by simply altering the current in the superconducting solenoid. Future use cases are hypothesised for bubble clusters, such as the production of new acoustic metamaterials and a new technique for the study of the nonlinear interaction of bubbles in an oscillating acoustic field.

The final section of this thesis describes a new experimental technique ‘Sonomaglev’. This new technique combines both acoustic and diamagnetic levitation, allowing for the manipulation of multiple levitated spherical water droplets, using a superconducting magnet fitted with low-power ultrasonic transducers. We show that multiple droplets, arranged horizontally along a line, can be stably levitated with this system, and demonstrate controlled contactless coalescence of two droplets. Numerical simulation of the magnetogravitational and acoustic potential reproduces the multiple stable equilibrium points observed in our experiments.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Hill, Richard Scase, Matthew
Keywords:	Fluid Mechancics, Levitation, Bubbles, Droplets, Diamagnetism
Subjects:	Q Science > QC Physics > QC501 Electricity and magnetism
Faculties/Schools:	UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID:	76672
Depositing User:	Hunter-Brown, George
Date Deposited:	31 Jan 2024 15:23
Last Modified:	31 Jan 2024 15:23
URI:	https://eprints.nottingham.ac.uk/id/eprint/76672

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