Production of air bubbles of a specified size

Abyss Aerosols: Drop Production from Underwater Bubble Collisions

Over the past century, drops production mechanisms from bubble bursting have been extensively studied. They include the centrifugal fragmentation of liquid ligaments from the bubble cap during film rupture, the flapping of the cap film, and the disintegration of Worthington jets after cavity collapse. We show here that a dominant fraction of previously identified as "surface bubble bursting" submicron drops are, in fact, generated underwater, in the abyss, inside the bubbles themselves before they have reached the surface. Several experimental evidences demonstrate that these drops originate from the flapping instability of the film squeezed between underwater colliding bubbles. This finding, emphasizing the eminent role of bubble-bubble collisions, alters fundamentally our understanding of fine aerosol production and opens a novel perspective for transfers across water-air interfaces.

The Effects of Reactant Concentration and Air Flow Rate in the Consumption of Dissolved O₂ during the Photochemistry of Aqueous Pyruvic Acid

The sunlight photochemistry of the organic chromophore pyruvic acid (PA) in water generates ketyl and acetyl radicals that contribute to the production and processing of atmospheric aerosols. The photochemical mechanism is highly sensitive to dissolved oxygen content, [O₂(aq)], among other environmental conditions. Thus, herein we investigate the photolysis (λ ≥ 305 nm) of 10–200 mM PA at pH 1.0 in water covering the relevant range 0 ≤ [O₂(aq)] ≤ 1.3 mM. The rapid consumption of dissolved oxygen by the intermediate photolytic radicals is monitored in real time with a dissolved oxygen electrode. In addition, the rate of O₂(aq) consumption is studied at air flow rates from 30.0 to 900.0 mL min⁻¹. For the range of [PA]₀ covered under air saturated conditions and 30 mL min⁻¹ flow of air in this setup, the estimated half-lives of O₂(aq) consumed by the photolytic radicals fall within the interval from 22 to 3 min. Therefore, the corresponding depths of penetration of O₂(g) into water (x = 4.3 and 1.6 µm) are determined, suggesting that accumulation and small coarse mode aqueous particles should not be O₂-depleted in the presence of sunlight photons impinging this kind of chromophore. These photochemical results are of major tropospheric relevance for understanding the formation and growth of secondary organic aerosol.

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

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.

Generation of microbubbles from hollow cylindrical ultrasonic horn

In this study, we found that microbubbles with diameters of less than 100μm can be easily generated by using a hollow cylindrical ultrasonic horn. Consecutive images of bubbles obtained by using high-speed and high-resolution cameras reveal that a capillary wave is formed on the gas-liquid interface under weak ultrasonic irradiation and that the wave head is detached in the form of bubbles by the fragmentation of the interface as the power of ultrasonic irradiation increases. Moreover, consecutive images of the bubble interface obtained by an ultra-high-speed camera indicate that the breakup of bubbles oscillating harmonically with the ultrasonic irradiation generates many microbubbles that are less than 100μm in diameter. With regard to the orifice diameter of the horn end, we found that its optimum value varies with the ultrasonic power input. When the orifice diameter is small, the capillary wave generated from the horn end easily propagates all over the gas-liquid interface, thereby starting the generation of microbubbles at a lower ultrasonic power input. When the orifice diameter is large, the capillary wave is attenuated because of viscosity and surface tension. Hence, in this case, microbubble generation from the horn requires a higher ultrasonic power input. Furthermore, the maximum yield of microbubbles via primary and secondary bubble generation can be increased by increasing the gas flow rate.

Red tide (Ptychodiscus brevis) toxin aerosols: a review

Advances in knowledge concerning red tide toxin aerosols (airborne) of the Florida red tide organism, Ptychodiscus brevis, have not kept pace with information about waterborne toxins. This review provides a summary of current knowledge regarding the characterization, effect and production of red tide toxin aerosols. Insight into the chemical characterization and toxic effects of aerosolized toxins is provided from investigations of toxins extracted from natural blooms, as well as from laboratory cultures, of P. brevis. This information is used in conjunction with the few studies that have been performed on toxin aerosols to consider toxic effects. The production of aerosolized toxins is considered through studies of jet drop aerosol formation from bursting bubbles. Existing information suggests that aerosolized red tide toxins may be the same chemicals as those extracted from laboratory cultures, with one of the toxins having a greater respiratory effect than others.

Droplet enrichment factors of pigmented and nonpigmented Serratia marcescens: possible selective function for prodigiosin

Drops produced by bursting bubbles provide a mechanism for the water-to-air transfer and concentration of matter. Bacteria can adsorb to air bubbles rising through bacterial suspensions and enrich the drops formed by the bubbles upon breaking, creating atmospheric biosols which function in dispersal. This bacterial enrichment can be quantified as an enrichment factor (EF), calculated as the ratio of the concentration of bacteria in the drop to that of the bulk bacterial suspension. Bubbles were produced in suspensions of pigmented (prodigiosin-producing) and nonpigmented cultures of Serratia marcescens. EFs for pigmented cultures were greater than EFs for nonpigmented cells. Pigmented cells appeared hydrophobic based on their partitioning in two-phase systems of polyethylene glycol 6000 and dextran T500. The surface hydrophobicity of pigmented cells may result from the hydrophobic nature of prodigiosin and could account for the greater ability of these bacteria to adsorb to air bubbles and enrich airborne droplets. Enhancement of the aerosolization of S. marcescens may be a selective function of the bacterial secondary metabolite prodigiosin.

Influence of Serratia marcescens Pigmentation on Cell Concentrations in Aerosols Produced by Bursting Bubbles

For eight strains of Serratia marcescens , increased cell concentrations were found in aerosols produced from bursting bubbles, with concentrations ranging from a maximum of ca. 80 times the bulk concentration for pigmented strains 4180, 933, and 274 to a minimum approximately equal to the bulk concentration for nonpigmented strain 8100. The increased cell concentration in the aerosol was suppressed when pigmented strains were grown at 37°C, a temperature at which the pigment prodigiosin is not synthesized, resulting in lower concentrations similar to those of nonpigmented strains. Strains that produce higher concentrations of prodigiosin after 1, 2, 4, and 8 days of growth show increasing concentrations in bubble-produced drops; duplicate cultures grown at 37°C did not show any increases. In four concurrent experiments, cells starved for 24 h showed greater concentrations than nonstarved cells for chromogenic strain NIMA, whereas for nonchromogenic strain WF, starved cells showed greater concentrations in three cases and a decreased concentration in the fourth. Bacterial concentrations in aerosol drops from bursting bubbles appear to be predominantly influenced by the surface condition of the bacterial cell.