Using Sound To Study the Effect of Frothers on the Breakaway of Air Bubbles at an Underwater Capillary

Abstract

Frothers, a class of surfactants, are widely employed in froth flotation to aid the generation of small bubbles. Their action is commonly explained by their ability to hinder coalescence. There are occasional references suggesting that the frother may also play a role in the initial breakup of the injected air mass. This work investigates the possible effect of the frother on breakup by monitoring air bubbles produced quasi-statically at an underwater capillary. Under this condition, breakup is isolated from coalescence and an impact of frothers on the detached bubble can be ascribed to an impact on breakup. The breakaway process was monitored by an acoustic technique along with high-speed cinematography. The results showed that the presence of frothers did influence the breakaway process and that the acoustic technique was able to detect the impact. It was demonstrated that the acoustic frequency and acoustic damping ratio depend upon the frother type and concentration and that they are associated with a liquid jet, which initially excites the bubble and then decays to form a surface wave. The addition of the frother did not influence the formation of the jet but did increase its decay rate, hence, dampening the surface wave. It is postulated that the action of the frother is related to an effect on the magnitude of surface tension gradients.

Adsorption and Desorption of a Phospholipid from Single Microbubbles under Pulsed Ultrasound Irradiation for Ultrasound-Triggered Drug Delivery

“…When microbubbles are exposed to low amplitude sound pressure fields the bubbles spherical vibrations synchronize with the pressure change, and the vibrational mode of the microbubbles depends on the sound pressure [18]. If the pressure amplitude increases, the vibrational mode shifts to a non-spherical mode with surface waves propagating on the bubble's surface.…”

“…Developments in ultrasound techniques have produced remarkable noninvasive and simple-to-use ultrasound imaging techniques, which enable the internal state of living bodies to be observed in real time. − Ultrasound techniques are widely used in medical diagnosis, and research is developing in the field of therapeutic techniques. − In ultrasound imaging techniques, microbubbles are injected into blood vessels and used as contrast agents to enhance image contrast. These microbubbles consist of an internal gas and a surrounding molecular film such as a lipid shell. , The internal gas is usually saturated with a volatile fluorocarbon, which acts as a poorly water-soluble osmotic agent and cosurfactant, thus improving the bubble stability and enabling control over the microbubble behavior. , The behavior of microbubbles under ultrasound irradiation is a basic characteristic of ultrasound imaging methods, in which signals reflected from the microbubbles are analyzed. − When microbubbles are exposed to low-amplitude sound pressure fields, the bubbles’ spherical vibrations synchronize with the pressure change, and the vibrational mode of the microbubbles depends on the sound pressure . If the pressure amplitude increases, the vibrational mode shifts to a nonspherical mode with surface waves propagating on the bubble’s surface.…”

“…15−17 When microbubbles are exposed to low-amplitude sound pressure fields, the bubbles' spherical vibrations synchronize with the pressure change, and the vibrational mode of the microbubbles depends on the sound pressure. 18 If the pressure amplitude increases, the vibrational mode shifts to a nonspherical mode with surface waves propagating on the bubble's surface. A further increase of the pressure amplitude induces intense vibrations, resulting in collapse of the microbubbles, accompanied by microjets of internal gas that penetrate the shell, because the shape of the bubbles cannot be maintained.…”

Investigation of the Effect of Electrolytes on the Breakaway of Air Bubbles at an Underwater Capillary Using High-Speed Cinematography and Passive Acoustic Techniques

“…In this process, air bubbles act as vehicles to selectively collect and transport valuable mineral particles from a mixed-particle suspension. To ensure the process efficiency, the bubbles must be small to provide larger interfacial area but, at the same time, have sufficient buoyancy to float the collected mineral particles [4][5][6][7]. A typical bubble size required ranges from 0.5 to 2.5 mm, but such bubble sizes are difficult to achieve in pure water because the lack of solutes cannot prevent coalescence [8][9][10].…”

“…Their observation was that the presence of solutes generally affects the break-up by producing smaller bubble sizes until a certain concentration is reached, after which the trend becomes adverse. To further explore the break-up phenomena, another study was carried out by the same group where air bubbles were slowly generated at a capillary tube in froth solutions under a quasi-static condition [4]. The experiment was monitored using high-speed cinematography and passive acoustic techniques allowing microscopic features associated with break-up to be revealed.…”