Levitated Bubbles Research Articles

Study on helium gas bubble levitation in high field superconducting magnet

The abnormal temperature rise and early quench often happened to the high field superconducting magnet, especially when the magnetic field is higher than 20 T. This phenomenon is attributed to helium gas bubbles levitation in the special high magnetic field environment. So, it is very important to accurately identify the formation and distribution of helium gas bubbles levitation for the development of high field superconducting magnet. In this paper, a new analytical method based on pressure is proposed to analysis the formation conditions and the spatial distribution of helium gas bubbles levitation. And a no-insulation REBCO insert coil was also developed to study the phenomenon of helium gas bubbles levitation. The REBCO insert coil was tested in high magnetic field produced by a water-cooled magnet. The new analytical method was used to simulate the formation conditions of helium gas bubbles levitation and the temperature distribution of the REBCO insert.

Toward Enhanced Aerosol Particle Adsorption in Never-Bursting Bubble via Acoustic Levitation and Controlled Liquid Compensation.

Bubbles in air are ephemeral because of gravity-induced drainage and liquid evaporation, which severely limits their applications, especially as intriguing bio/chemical reactors. In this work, a new approach using acoustic levitation combined with controlled liquid compensation to stabilize bubbles is proposed. Due to the suppression of drainage by sound field and prevention of capillary waves by liquid compensation, the bubbles can remain stable and intact permanently. It has been found that the acoustically levitated bubble shows a significantly enhanced particle adsorption ability because of the oscillation of the bubble and the presence of internal acoustic streaming. The results shed light on the development of novel air-purification techniques without consuming any solid filters.

Bubbling of Ferrofluid Droplets via Coupled Magnetic and Sound Fields (Adv. Mater. Interfaces 7/2023)

Ferrofluid Bubble Formation In article number 2201724 by Kangqi Liu, Yuan Gao, Duyang Zang, and colleagues, a ferrofluid drop was turned into a bubble in a controlled manner by coupling the effect of magnetic and sound fields. The acoustically levitated bubble can serve as an ideal template for evaporation-induced assembly.

Bubbling of Ferrofluid Droplets via Coupled Magnetic and Sound Fields

AbstractBubbles play essential roles in many natural and industrial processes because of the unique effects of their films on heat–mass transfer and their soft confined geometry for interfacial assembly or phase transitions. Here, a technique for noncontact bubbling via coupling of sound and magnetic fields in acoustic levitation is reported. An acoustically levitated ferrofluid droplet can be transformed into a closed bubble in a controlled manner. It has been found that the magnetic field pulls the flattened ferrofluid film downward, and making it deviate from its initial levitation position determined by the balance between acoustic radiation force and gravity. This results in variation in acoustic radiation pressure on the film surface and generates an upwards torque on the levitated film, leading to buckling and subsequent bubble transition via acoustic resonance. Moreover, the levitated ferrofluid bubble can remain unburst in the sound field for minutes to enable its complete evaporation; thus, solid hollow shells form. This work provides insight for understanding the coupled effect of sound and magnetic fields on ferrofluid drops and sheds light on evaporation‐driven self‐assembly of ferrofluid particles into shell structures

Sonoluminescence as a probe of conditions during cavitation

Acoustic cavitation occurs in all liquids irradiated with sufficient intensity of sound or ultrasound. The collapse of such bubbles creates local heating and provides a unique source of energy for driving chemical reactions. In addition to sonochemical bond scission and formation, cavitation also induces light emission in many liquids. This phenomenon of sonoluminescence (SL) and has captured the imagination of many researchers since it was first observed 85 years ago. SL provides a direct probe of cavitation events and has provided most of our understanding of the conditions created inside collapsing bubbles. Spectroscopic analyses of SL from single acoustically levitated bubbles as well as from clouds of bubbles have revealed molecular, atomic, and ionic line and band emission riding atop an underlying continuum arising from radiative plasma processes. These studies permit quantitative measurement of the intracavity conditions: relative peak intensities for temperature measurements, peak shifts and broadening for pressures, and peak asymmetries for plasma electron densities. Extraordinary conditions are generated inside the collapsing bubbles in ordinary room-temperature liquids – observable temperatures exceeding 15 000 K, pressures >1000 bar, and heating and cooling rates in excess of 1012 K/s. For clouds of cavitating bubbles, multibubble sonoluminescence (MBSL) reveal slightly more moderate local conditions inside bubble clouds of ∼5000 K, ∼300 atm. Biomedical applications of SL will be discussed.

Analysis of bubble management at different gravity levels by means of an acoustic field

Multiphase flows management is a major challenge in many space applications given the different gravity levels involved. While many of the numerical investigations of liquid-gas phenomena deal with the radial bubble behavior and thus the heat exchange, only a few studies have been conducted on the translational motion of bubbles. We present a numerical investigation of the translational motion of gas bubbles immersed in a liquid that is subject to an acoustic wave at different gravity levels. In the computation, the equations for radial oscillation and translational motion are solved simultaneously. The dynamics of bubbles at different gravity levels (from microgravity to hypergravity) are discussed. Bubbles can be trapped by the acoustic wave at levitation positions in different scenarios. The dependence of the levitation position on the initial bubble position at different pressure amplitudes has been computed, giving rise to the bubble being directed to different nodes of the acoustic wave. The bubble radius also determines if and where the bubble levitates. We propose an analytical criterion for the capture of bubbles in a levitation position in terms of a new dimensionless parameter. The criterion is based on the balance between the average acoustic force and the buoyancy force. With the proposed criterion, the position of bubble levitation can be calculated analytically for any scenario.

Bubble Control, Levitation, and Manipulation Using Dielectrophoresis

AbstractBubbles attached to surfaces are ubiquitous in nature and in industry. However, bubbles are problematic in important technologies, including causing damage to the operation of microfluidic devices and being parasitic during heat transfer processes, so considerable efforts have been made to develop mechanical and electrical methods to remove bubbles from surfaces. In this work, liquid dielectrophoresis is used to force a captive air bubble to detach away from an inverted solid surface and, crucially, the detached bubble is then held stationary in place below the surface at a distance controlled by the voltage. In this “levitated” state, the bubble is separated from the surface by liquid layer with a voltage‐selected thickness at which the dielectrophoresis force exactly counterbalances the gravitational buoyancy force. The techniques described here provide exceptional command over repeatable cycles of bubble detachment, levitation, and reattachment. A theoretical analysis is presented that explains the observed detachment–reattachment hysteresis in which bubble levitation is maintained with voltages in an order of magnitude lower than those used to create detachment. The precision surface bubble removal and control concepts are relevant to situations such as nucleate boiling and microgravity environments and offer an approach toward “wall‐less” bubble microfluidic devices.

The Chemical History of a Bubble.

Acoustic cavitation (the growth, oscillation, and rapid collapse of bubbles in a liquid) occurs in all liquids irradiated with sufficient intensity of sound or ultrasound. The collapse of such bubbles creates local heating and provides a unique source of energy for driving chemical reactions. In addition to sonochemical bond scission and formation, cavitation also induces light emission in many liquids. This phenomenon of sonoluminescence (SL) has captured the imagination of many researchers since it was first observed 85 years ago. SL provides a direct probe of cavitation events and has provided most of our understanding of the conditions created inside collapsing bubbles. Spectroscopic analyses of SL from single acoustically levitated bubbles as well as from clouds of bubbles have revealed molecular, atomic, and ionic line and band emission riding atop an underlying continuum arising from radiative plasma processes. Application of spectrometric methods of pyrometry and plasma diagnostics to these spectra has permitted quantitative measurement of the intracavity conditions: relative peak intensities for temperature measurements, peak shifts and broadening for pressures, and peak asymmetries for plasma electron densities. The studies discussed herein have revealed that extraordinary conditions are generated inside the collapsing bubbles in ordinary room-temperature liquids: observable temperatures exceeding 15 000 K (i.e., three times the surface temperature of our sun), pressures of well over 1000 bar (more than the pressure at the bottom of the Mariana Trench), and heating and cooling rates in excess of 1012 K·s-1. Scientists from many disciplines, and even nonscientists, have been and continue to be intrigued by the consequences of dynamic bubbles in liquids. As chemists, we are fascinated by the high energy reactions and processes that occur during acoustic cavitation and by the use of SL as a spectroscopic probe of the events during cavitation. Within the chemical realm of SL and cavitation there are many interesting questions that are now answered but also many that remain to be explored, so we hope that this Account reveals to the reader some of the most fascinating of those curiosities as we explore the chemical history of a bubble. The high energy species produced inside collapsing bubbles also lead to secondary reactions from the high energy species created within the collapsing bubble diffusing into the bulk liquid and expanding the range of sonochemical reactions observed, especially in redox reactions relevant to nanomaterials synthesis. Bubbles near solid surfaces deform upon collapse, which lessens the internal heating within the bubble, as shown by SL studies, but introduces important mechanical consequences in terms of surface damage and increased surface reactivity. Our understanding of the conditions created during cavitation has informed the applications of ultrasound to a wide range of chemical applications, from nanomaterials to synthetically useful organic reactions to biomedical and pharmaceutical uses. Indeed, we echo Michael Faraday's observation concerning a candle flame, "There is not a law under which any part of this universe is governed which does not come into play and is touched upon in these phenomena." ( Faraday , M. The Chemical History of a Candle ; Harper & Brothers : New York , 1861 ).

From underwater thunder to cavitation from pulsed ultrasound: One graduate student’s perspective of the years leading up to the formation of NCPA

The Physical Acoustics Research Group at the University of Mississippi (PARGUM) fostered a vibrant, multidisciplinary research environment in the early 1980s that incubated the concept of the National Center for Physical Acoustics (NCPA). It also provided graduate students, new to physical acoustics, an enticing glimpse into the breadth of the field and an exposure to a range of important contemporary problems. The research programs included terrestrial lightning detection and location, the underwater sound generated by lightning striking the ocean surface, long range sound propagation, propagation through porous materials, sound amplification by selective molecular excitation, acoustic levitation of bubbles and droplets, studies of acoustic cavitation thresholds and sonoluminescence, numerical simulation of bubble dynamics, and others. Beyond the scientific activities, PARGUM introduced a number of new acousticians to the ASA, many of whom have contributed to the leadership of the Society. The purpose of this presentation is to review some of the research results produced by the members of group from the time period as well as their contributions to the ASA.

Acoustic levitation of soap bubbles in air: Beyond the half-wavelength limit of sound

We report on the behavior of levitated soap bubbles in a single-axis acoustic field. For a single bubble, its surface in the polar regions is under compression, but in the equatorial region, it is under suction. Levitation becomes unstable when the height of the bubble approaches half the wavelength of the sound wave because horizontal fluctuations lead to a negative recovery force and a negative levitation force. Vertically stacked double bubbles notably can be stable under levitation if their total vertical length is ∼5λ/6, significantly beyond λ/2 in consequence of the formation of a toroidal high-pressure region around the waist of the two bubbles. Our results provide a deeper insight into the stability of acoustic levitation and the coupling between bubbles and sound field.

Diffusion of Small Gas Bubbles into Liquid Studied by the Rotary Chamber Technique

AbstractThe rotary chamber technique is capable of observing small levitated bubbles in liquid for various research purposes. The present paper focuses on diffusion of a small spherical bubble into undersaturated water. The decaying bubble size is recorded in time by image processing. The results are plotted as Sherwood versus Reynolds number where the Schmidt number is of order 300. Similarity is found for each of four gases in water. The boundary layer prediction Sh $ \propto \sqrt {{\rm{Re}}} $ is confirmed in general. A physically accountable model provides a good representation of results.

Bubble oscillations and motion under vibration

Bubbles under vibration can behave in unusual ways, e.g., moving downward against the force of buoyancy. While the bubble downward motion due to the Bjerknes force is well known at acoustic frequencies close to the bubble resonant frequency, these experiments demonstrate that these effects can be observed at relatively low frequencies as well. Experiments were performed in a thin, quasi-two-dimensional rectangular acrylic box partially filled with 20-cSt PDMS silicone oil with overlying ambient air. The apparatus was subjected to sinusoidal axial vibration that produced breakup of the gas-liquid free surface, producing liquid jets into the air, droplets pinching off from these jets, gas cavities in the liquid from impacts of these droplets, and bubble transport below the interface. Vibration conditions for the attached videos are 280 Hz frequency, 15 g acceleration, and 94 micron peak-to-peak displacement. Behaviors shown in the videos include the following. 1. Free surface breakup into jets and droplets, and formation of bubbles under the free surface. 2. Bubbles thus generated moving downward in the cell. 3. Bubbles attracted to the first bubble deep in the cell and eventually merging to form a large bubble at the base of the cell. 4. Bubble cluster at the base of the cell merging to form a larger bubble, which stabilizes at a levitated location below the free surface and acts to damp out the surface breakup. 5. The levitated bubble interface and its breakup are similar to the free surface breakup into jets and droplets, but the jets in the bubble are facing downward. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Radial and translational oscillations of an acoustically levitated bubble in aqueous ethanol solutions

The radial and translational oscillations of a single cavitation bubble in a standing ultrasound wave were investigated experimentally at various driving acoustic pressures for aqueous ethanol solutions with different bulk molar fractions of ethanol range of 0-1.3 × 10(-3). The results show that both the lower and upper stability thresholds of the acoustic driving pressure decreased as the concentration of ethanol was increased. At a given driving pressure the ambient and maximum bubble sizes increased with increasing ethanol concentration. In addition, as the ethanol was increased, the sonoluminescence intensity decreased while the bubble dynamics remained largely unchanged. The translational oscillation of the levitated bubble, however, became increasingly violent with increasing ethanol concentration. The displacement of the bubble reached 0.7 mm at the highest concentration studied (1.3 × 10(-3)) and the maximum bubble size was found to change as the bubble jumped up and down. This bubble translation may be responsible for the decrease of the acoustic driving pressure threshold and suggests that repetitive injection of ethanol molecules into the bubble takes place. These results may account for the different sensitivities of single bubble and multi-bubble sonoluminescence to the presence of volatile additives.

Bubbles, surfactants, shape oscillations, optical levitation, and light scattering: a survey

Research emphasizing relatively slow aspects of bubble dynamics will be summarized. Though the attention is mainly on acoustically levitated bubbles larger than the size for monopole resonance, early experiments on stable optical levitation of gas bubbles in water [J. Acoust. Soc. Am. 83, 970-975 (1988)] will also be noted as well as fundamental aspects of light scattering by bubbles [J. Opt. Soc. Am. and/or Applied Optics (1979-1991)]. Modulated radiation pressure was demonstrated to be an effective way for mode-specific excitation of shape oscillations of acoustically levitated bubbles [J. Acoust. Soc. Am. 93, 706-713 (1993)]. The damping of shape oscillations was demonstrated to be strongly influenced by the presence of insoluble or soluble surfactants [J. Fluid Mech. 300, 149-167 (1995); Phys. Rev. Let. 75, 2686-2689 (1995); J. Acoust. Soc. Am. 102, 3372-3377 (1997)]. A convenient way of measuring the damping was to use laser beam extinction to monitor freely decaying shape oscillations. This technique was sufficiently sensitive to reveal the strong dependence of the damping on surface elasticity. Even for clean bubbles, an improved analysis of the damping was needed. [Sponsored in part by NASA and by ONR.]

Levitation of air bubbles and slugs in liquids under low-frequency vibration excitement

This experimental study reports the influence of low-frequency vibrations, in the range of 60–400 Hz, on the rise of single air bubbles and slugs injected into two columns (of diameters 0.014 and 0.05 m), filled with liquids of varying densities (in the range 889– 1381 kg m - 3 ) and viscosities (in the range 0.48–1.4 Pa s). For a specified set of operating conditions the bubbles or slugs can be made to levitate, i.e. held stationary in the column. The height of the liquid, h, above the position at which the gas bubble is levitated was determined for a wide range of operating conditions (vibration frequency and amplitude, operating pressure, column diameter, liquid density and viscosity). The experimentally determined values of h are in good agreement with the theoretical model of Baird [1963a. Resonant bubbles in a vertically vibrating column. Canadian Journal of Chemical Engineering 41, 52–55].

Levitation of air bubbles in liquid under low frequency vibration excitement

This experimental study reports the influence of low frequency vibrations, in the range of 50–250 Hz, on the rise of single gas bubbles injected into a column of liquid. Water and a high-viscosity hydrocarbon-oil were used as the liquid phase. For a specified set of operating conditions the bubble can be made to levitate, i.e. held stationary in the column. The bubbles employed had volumes that varied from 0.01 to 0.6 mL. The height of the liquid, h, above the position at which the bubble is levitated was determined for a wide range of operating conditions (bubble volume V b , vibration frequency, f, pressure above the liquid surface, P, and the vibration amplitude, λ ). The experimental values of h are in good agreement with the theoretical model of Baird (1963. Resonant bubbles in a vertically vibrating column. Canadian Journal of Chemical Engineering 41, 52–55).

INFLUENCE OF SONOCHEMISTRY ON SINGLE-BUBBLE SONOLUMINESCENCE

Spherical oscillation of an acoustically levitated gas bubble in water was simulated numerically to elucidate the phenomenon of single-bubble sonoluminescence (SBSL). A refined hydro-chemical model was used, which took into account the processes of water vapor evaporation and condensation, mass diffusion, and chemical reactions. The numerical results show significant water vapor dissociations but rather low degrees of ionizations. A widely accepted weakly ionized gas model is then used to compute the light emission. Contrary to earlier predictions without chemical reactions, the present calculated light spectra are generally too small and the pulses are too short to fit to recent experimental results within stable SBSL range. To solve this contradiction, the electrostatic interactions of the ionized gases are included, which is shown to lower the ionization potentials of gas species in the bubble significantly.

Precise measurement technique for the stable acoustic cavitation bubble

Based on the periodic oscillation of the stable acoustic cavitation bubble, we present a precise measurement technique for the bubble evolution. This technique comprises the lighting engineering of pulsing laser beam whose phase can be digitally shifted, and the long distance microphotographics. We used a laser, an acousto-optic modulator, a pulse generator, and a long distance microscope. The evolution of a levitated bubble can be directly shown by a series of bubble’s images at different phases. Numerical simulation in the framework of the Rayleigh-Plesset bubble dynamics well supported the experimental result, and the ambient radius of the bubble, an important parameter related to the mass of the gas inside the bubble, was obtained at the same time.

Viscous forces on acoustically levitated gas bubbles

When a gas bubble is subjected to an oscillating acoustic field in a gravitational environment, it seeks a location where time-averaged net force vanishes (‘acoustic levitation’). At this location, the bubble undergoes periodic, coupled volumetric pulsation and translational motion. In this study, we extend the existing inviscid theory of acoustic levitation to include viscous drag forces arising from translational motion. Equilibrium locations are computed and compared with predictions from inviscid theory. It is found that the effects are quite small, producing negligible effect on the levitation position.

Sonoluminescence in varying acceleration environments

In order to prepare for experiments in variable-g environments, some of the multiple effects caused by the time-varying acceleration of acoustic resonators used in bubble levitation experiments are considered. The coupled effects of the induced changes in ambient pressure (due to a changing hydrostatic head) and bubble position (due to a change in buoyant body force) were modeled. Changing the ambient pressure, while holding the acoustic pressure amplitude constant, causes changes in the radial bubble response and diffusive equilibrium requirements. Changing the bubble levitation position causes both the local acoustic pressure amplitude and gradient to change, which will again impact bubble response. If the bubble remains in a stable diffusive equilibrium, both of these effects will force the bubble’s equilibrium radius to change. By using an empirical relation for emitted sonoluminescence intensity versus bubble response, the variation of emitted light intensity as a function of the changing ambient acceleration can be predicted. The predicted results are shown to agree quantitatively with existing experimental data from other research groups. An experiment was designed and built to fly onboard a KC-135 aircraft that has been reinforced for parabolic flight maneuvers to simulate micro and hyper gravity acceleration. Thesis advisor: R. Glynn Holt Copies of this thesis may be obtained by contacting the advisor, Glynn Holt, Dept. of Aerospace and Mechanical Engineering, Boston University, 110 Cummington St., Boston, MA 02215. E-mail address: rgholt@bu.edu