Single oscillating bubbles

Observed radius time curve for a single oscillating bubble in pure water using the single bubble levitation system at 26.73 kHz (temperatures between —0.5 and 1.1°C). 

A detailed study of the nucleation of ice by power ultrasoimd has been performed using a variety of high-speed photography systems with a particular focus on the influence of cavitation. The nucleation of ice has been shown to occur predominantly within the bubble cloud produced by a commercial ultrasonic horn. An investigation of a single oscillating bubble has confirmed that ice crystals are nucleated in the immediate vicinity of the bubble. 

It is widely thought that the high pressure emitted from a "transient" cavitation bubble is responsible for the nucleation process (Hickling, 1994) however, experiments utilizing a single oscillating bubble have shown that ice can be initiated by a "stable" cavitation bubble. The mechanism of nucleation may be related to the asymmetric bubble shape, the flow field associated with the cavitation bubble, or the production of microbubbles. 

Marmottant P, Hilgenfeldt S (2003) Controlled vesicle deformation and lysis by single oscillating bubbles. Nature 423 153... 

These results were in contrast to the previous experiments described above, where nucleation was always observed. It is thought that as nucleation is a stochastic process, a single oscillation of a laser-induced bubble may not always lead to the nucleation. The probability of nucleation is increased by the continuously oscillating bubble produced by the standing wave system, and it is increased further by the multicavitation events produced by the ultrasonic horn. 

Under the appropriate conditions, the acoustic force on a bubble can be used to balance against its buoyancy, holding the bubble stable in the liquid by acoustic levitation. This permits examination of the dynamic characteristics of the bubble in considerable detail, from both a theoretical and an experimental perspective. Such a bubble is typically quite small compared to an acoustic wavelength (e.g., at 20 kHz, the resonance size is approximately 150 pm). For rather specialized but easily obtainable conditions, a single, stable, oscillating gas bubble can be forced into such large-amplitude pulsations that it produces sonoluminescence emissions on each (and every) acoustic cycle. Such SBSL is outside the scope of this chapter. 

In order to study the mechanism by which a cavitation bubble may stimulate ice crystallization, a standing wave system was used to levitate a single bubble in a fixed location within pure water. It was found that the nucleation of ice could only be stimulated at a higher nucleation temperature in the presence of the oscillating cavitation bubble (Chow et al., 2004). 

In upflow operation the liquid to particle Sherwood number is higher than in downflow operation and increases remarkably with gas flow, indicating the large contribution of the liquid turbulence caused by bubble motion. Recently attempts were made to analyse the situation also theoretically and a unified correlation has been developed for heat and mass transfer from single spheres, packed beds as well as tube wall, taking into account the diffusion of solute into a liquid film,oscillating with response to the bub-... 

Fig. 1.4 Theoretical data shown mass of evaporated from bubble surface during a single expansion phase at various frequencies. It could be seen that the mass that could evaporate exceeds the amount present in a monolayer on the bubble surface at lower frequencies. At higher frequencies, the amount that could evaporate is less than a monolayer, which is due to very short expansion time available during bubble oscillations. Further details are available in Ref [101]...

There is a now an array of experimental techniques that can be used to measure d5mamic surface tensions, y(t), including maximum bubble pressure (MBP), oscillating jet, inclined plate, drop volume, drop shape, and overflowing cylinder (OFC).i With the aid of an appropriate equation of state, it is possible to infer the d5uiamic surface excess, F(0. Uncertainty in the adsorption isotherm can lead to problems in the interpretation of DST data and incorrect conclusions as to the adsorption mechanisms. A more direct approach is to measure ( ) itself by neutron reflection (NR), or ellipsometry. ii Here we review the state of the art, with particular attention to recent results on model single-chain cationic surfactants... 

A variety of swirl motions are known to occur in a bath agitated by gas injection when the bath surface is exposed to the atmosphere, as described in Sect. 5.2.1.4 [18,23, 29-37]. In particular, two types of swirl motions typically occur in a circular cylindrical bath agitated by single-nozzle bottom gas injection, as schematically illustrated in Fig. 5.6 [29, 30] One is observed over an aspect ratio, H /D, from approximately 0.2-1.0. The other appears for H /D > 2. No swirl motion occurs when the aspect ratio falls in the range of 1.0-2.0. The former swirl motion is caused by bath surface oscillations due to quasi-periodic generation and subsequent arrival of bubbles at the bath surface. It resembles the rotary sloshing of a water bath contained in a circular cylindrical vessel [16,17,38]. The latter is caused by the Coanda effect [26], which appears when a bubbling jet approaches the side wall of the vessel [29,30,39]. 

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