Oscillation and breakup of a bubble under forced vibration

Movassat, Mohammad; Bussmann, Markus

doi:10.1016/j.ijheatfluidflow.2015.05.014

Cited by 14 publications

(13 citation statements)

References 23 publications

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“…These distortions appear similar to the chaotic oscillations that are often observed in vibrated bubbles shortly before jetting (Movassat 2012). In the 1.04 MHz atomization video (figure 4 a ), it was noted that the top drop in the chain changes from transparent to opaque immediately before atomization, which would suggest that some sort of surface instability, such as capillary waves, contributes to atomization.…”

Section: Discussionsupporting

confidence: 70%

Ultrasonic atomization of liquids in drop-chain acoustic fountains

et al. 2015

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When focused ultrasound waves of moderate intensity in liquid encounter an air interface, a chain of drops emerges from the liquid surface to form what is known as a drop-chain fountain. Atomization, or the emission of micro-droplets, occurs when the acoustic intensity exceeds a liquid-dependent threshold. While the cavitation-wave hypothesis, which states that atomization arises from a combination of capillary-wave instabilities and cavitation bubble oscillations, is currently the most accepted theory of atomization, more data on the roles of cavitation, capillary waves, and even heat deposition or boiling would be valuable. In this paper, we experimentally test whether bubbles are a significant mechanism of atomization in drop-chain fountains. High-speed photography was used to observe the formation and atomization of drop-chain fountains composed of water and other liquids. For a range of ultrasonic frequencies and liquid sound speeds, it was found that the drop diameters approximately equalled the ultrasonic wavelengths. When water was exchanged for other liquids, it was observed that the atomization threshold increased with shear viscosity. Upon heating water, it was found that the time to commence atomization decreased with increasing temperature. Finally, water was atomized in an overpressure chamber where it was found that atomization was significantly diminished when the static pressure was increased. These results indicate that bubbles, generated by either acoustic cavitation or boiling, contribute significantly to atomization in the drop-chain fountain.

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Section: Discussionsupporting

confidence: 70%

Ultrasonic atomization of liquids in drop-chain acoustic fountains

et al. 2015

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“…In terms of bubble dynamics, the resistance to change in velocity (inertia) of the liquid penetrates the centre of the bubble, altering the bubble volume [ 25 ], until the liquid penetrates the entire sphere breaking it up into smaller bubbles. Jagannathan et al [ 26 ] observed rapid fragmentation of bubbles at high frequencies as a result of the cavitation and subsequent deformation of the larger bubbles, which is in accordance with the research conducted by Movassat et al [ 24 ]. Although the behaviour of a bubble subjected to oscillating fields has been investigated, mass preparation of bubbles has not been reported using this method.…”

Section: Introductionsupporting

confidence: 86%

“…For instance, setting the DC voltage to 5 kV with a superimposed AC voltage of 4 kV P–P oscillates the waveform between 3 kV and 7 kV. Depending on the applied frequency and amplitude, the droplets undergo non-linear oscillations, which then results in their break-up [ 24 ]. Balachandran et al [ 22 ] superimposed AC on DC electric field to facilitate liquid droplet formation in their electrospraying apparatus.…”

Section: Introductionmentioning

confidence: 99%

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Novel Preparation of Monodisperse Microbubbles by Integrating Oscillating Electric Fields with Microfluidics

et al. 2018

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Microbubbles generated by microfluidic techniques have gained substantial interest in various industries such as cosmetics, food engineering, and the biomedical field. The microfluidic T-junction provides exquisite control over processing parameters, however, it relies on pressure driven flows only; therefore, bubble size variation is limited especially for viscous solutions. A novel set-up to superimpose an alternating current (AC) oscillation onto a direct current (DC) field is invented in this work, capitalising on the possibility to excite bubble resonance phenomenon and properties, and introducing relevant parameters such as frequency, AC voltage, and waveform to further control bubble size. A capillary embedded T-junction microfluidic device fitted with a stainless-steel capillary was utilised for microbubble formation. Furthermore, a numerical model of the T-junction was developed by integrating the volume of fluid (VOF) method with the electric module; simulation results were attained for the formation of the microbubbles with a particular focus on the flow fields along the detachment of the emerging bubble. Two main types of experiments were conducted in this framework: the first was to test the effect of applied AC voltage magnitude and the second was to vary the applied frequency. Experimental results indicated that higher frequencies have a pronounced effect on the bubble diameter within the 100 Hz and 2.2 kHz range, whereas elevated AC voltages tend to promote bubble elongation and growth. Computational results suggest there is a uniform velocity field distribution along the bubble upon application of a superimposed field and that microbubble detachment is facilitated by the recirculation of the dispersed phase. Furthermore, an ideal range of parameters exists to tailor monodisperse bubble size for specific applications.

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“…Smaller bubble sizes can be achieved at lower absolute DC voltage magnitudes by adjusting the tip-to-collector distance to increase the electric field strength. Movassat et al 31 modelled the oscillatory behaviour of a bubble when subjected to large vibrations. The bubble begins to deform, resulting in the formation of a dimple in its centre as shown in figure 8a.…”

Section: Effect Of Varying Electric Field Strengthmentioning

confidence: 99%

Effect of the Mixing Region Geometry and Collector Distance on Microbubble Formation in a Microfluidic Device Coupled with ac–dc Electric Fields

et al. 2019

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In this work we report a significant advance in the preparation of monodisperse microbubbles using a combination of microfluidic and electric field technologies. Microbubbles have been employed in various fields such as biomedical engineering, water purification and food engineering. Many techniques have been investigated for their preparation. Of these, the microfluidic T-Junction has shown great potential due to the high degree of control it has over processing parameters and the ability to produce monodisperse microbubbles. Two main lines of investigation were conducted in this work-the effect of varying the mixing region distance (Mx) and the influence of altering the tip-tocollector distance (Dx) when an AC-DC field is applied. It was found that when Mx was decreased from 200µm to 100µm, the microbubble size also decreased from 128 ± 3 µm to 88 ± 5 µm due to an increase in shear stress as a result of a reduction in surface area. Similarly, decreasing the tip-tocollector distance results in an increase in electric field strength experienced at the nozzle, facilitating further reduction of bubble size from 111 ± 1 µm to 86 ± 1µm at an AC voltage of 6kV P-P and an applied DC voltage of 6kV. Experiments conducted with the optimal parameters identified from the previous experiments enabled further reduction of the microbubble size to 18 ± 2 µm. These results suggest that a unique combination of parameters can be employed to achieve particular microbubble sizes to suit various applications.

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Oscillation and breakup of a bubble under forced vibration

Cited by 14 publications

References 23 publications

Ultrasonic atomization of liquids in drop-chain acoustic fountains

Ultrasonic atomization of liquids in drop-chain acoustic fountains

Novel Preparation of Monodisperse Microbubbles by Integrating Oscillating Electric Fields with Microfluidics

Effect of the Mixing Region Geometry and Collector Distance on Microbubble Formation in a Microfluidic Device Coupled with ac–dc Electric Fields

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