Film Drop Research Articles

Dust Formation by Bubble-burst Phenomenon at the Surface of a Liquid Steel Bath

We have developed an experimental device for studying the main mechanism of dust formation in electric arc furnace steelmaking: the burst of gas bubbles at the liquid steel surface. As in the case of the air-water system, the bubble-burst process takes place in three steps: breaking of the film cap, projection of film drops, and projection of jet drops. The film break and the jet drop formation are observed with a high-speed video camera. The film drop aerosol enters a particle counter, which characterizes the drops in size and number. Results are presented and discussed. The quantification of both types of projections leads to the conclusion that the film drop projections represent the major source of dust. The amount of film drops greatly decreases with the parent bubble size. Bubbles with diameter under 4 mm theoretically do not produce film drops. Decreasing the CO-bubble size enough would therefore represent an effective solution for reducing drastically the electric arc furnace dust emission.

Droplet production from disintegrating bubbles at water surfaces. Single vs. multiple bubbles

We experimentally determine the droplet production rate at a water surface where either single or multiple bubbles (bubbly flow) with similar mean diameters disintegrate and produce film and jet droplets. A detailed assessment of film drop production from bubbly flow is important, since most presently used correlations are based on single-bubble measurements. Moreover, jet drops––even though they contain a much larger fluid volume––are de-entrained into the water surface in most technical and geophysical applications. Detailed phase Doppler anemometry (PDA) measurements are performed in the vicinity of the water surface with long sampling times. For a considered mean diameter of approximately 3 mm, the size distribution of the non spherical bubbles is determined from photographic images. From single-bubble measurements we find, consistent with literature data, a narrow size distribution of the jet drops with a mean diameter of 477 μm. For bubbly flow, the maximum is shifted to somewhat smaller jet drop diameters (425 μm) and the production of film droplets increases significantly. We relate this increase to the coalescence of bubbles prior to their disintegration at the surface. Our results therefore show that for a fixed bubble size and gas flow rate the number of film drops entrained from a bubbly flow is underestimated, if the estimate is based on single-bubble data.

Chemical composition and sources of the high Arctic aerosol relevant for cloud formation

The chemical composition, sources, and methods of production of cloud condensation nuclei (CCN) were studied over the pack ice covered Arctic Ocean in summer. After ∼2 days' travel of air over the pack ice, two local CCN sources were identified: particles derived from the bursting bubbles on open water between ice floes (film and jet drops) and particles reaching CCN size by acquisition of oxidation products of dimethyl sulfide. The bubble‐derived particle modes were found to have an exponential dependence on prevailing wind speed. The film drop generation depended less on wind speed and jet drop production depended more on wind speed than particles over open water did. However, the enhanced presence of film drop particles at wind speeds <5 m s−1 suggested a source of bubbles, other than wind, that is most active during clear sky days and ice melting. The film drop particles were mainly organic in nature, but their sea‐salt component increased at high wind speeds >12 m s−1 to dominate both mass and number. The jet drop mode was composed largely of sea salt, making a significant mass contribution already for wind speeds >5 m s−1. However, the smaller‐sized jet drops were not pure sodium chloride but contained a varied and appreciable organic component. The sulfur‐containing particles dominated the CCN population and mass for the most common wind speeds of 5–12 m s−1. Measured CCN concentrations were on average less than would have been expected from either a sulfate or a sea‐salt composition and the observed particle‐size distribution. It is concluded that other components, probably organic, depressed the nucleating ability of the particles. However, on clear sky days, there were a majority of occasions on which CCN concentrations were more than predicted from a sulfate composition and the measured size distribution.

Cloud‐active particles over the central Arctic Ocean

Concentrations of cloud condensation (CCN) and ice forming nuclei (IFN) were measured throughout an expedition by icebreaker around the central Arctic Ocean including the North Pole from July 15 to September 23, 1996. Daily median CCN concentrations at 0.25% supersaturation were typically in the range 15 to 50 cm−3, but concentrations varied by 3 orders of magnitude over the expedition and commonly by an order of magnitude within a day. They were highest near the ice edge and fell by almost an order of magnitude in the first 36 hours of transport from the open sea into the pack ice region. For longer transport times they increased again indicating a local source, suggested to be drops injected into the air by bubbles bursting on open leads. Median concentrations of IFN ranged from 18 m−3 just inside the pack ice at the beginning of the expedition to 1 m−3 at the end. The differences with transport time from the ice edge were less marked than for CCN. Comparison of CCN measurements with simultaneously measured number size distributions showed that the median concentration active at a given supersaturation was only 71% of the number expected if all the particles had been composed of pure ammonium sulfate. Transmission electron microscope observations of individual particles suggested an evolution of many CCN from nonvolatile, nonhygroscopic particles <50 nm by acquisition of the oxidation products of dimethyl sulfide. Cloud processing added further mass. The largest primary source within the pack ice region was deduced to be film drops from bursting bubbles yielding liquid particles with a high organic content and surfactant properties. A relationship between CCN number and sulfur mass is derived which extends previous results to lower CCN numbers and indicates a greater sensitivity to change in sulfate mass than at lower latitudes. Bacteria and probable submicron fragments of marine organisms were identified in the samples and suggested to be the source of IFN.

Turbulent aerosol fluxes over the Arctic Ocean: 2. Wind‐driven sources from the sea

An eddy‐covariance flux system was successfully applied over open sea, leads and ice floes during the Arctic Ocean Expedition in July‐August 1996. Wind‐driven upward aerosol number fluxes were observed over open sea and leads in the pack ice. These particles must originate from droplets ejected into the air at the bursting of small air bubbles at the water surface. The source flux F (in 106 m−2 s−1) had a strong dependency on wind speed, and , over the open sea and leads, respectively (where is the local wind speed at about 10 m height). Over the open sea the wind‐driven aerosol source flux consisted of a film drop mode centered at ∼100 nm diameter and a jet drop mode centered at ∼1 μm diameter. Over the leads in the pack ice, a jet drop mode at ∼2 μm diameter dominated. The jet drop mode consisted of sea‐salt, but oxalate indicated an organic contribution, and bacterias and other biogenic particles were identified by single particle analysis. Particles with diameters less than −100 nm appear to have contributed to the flux, but their chemical composition is unknown. Whitecaps were probably the bubble source at open sea and on the leads at high wind speed, but a different bubble source is needed in the leads owing to their small fetch. Melting of ice in the leads is probably the best candidate. The flux over the open sea was of such a magnitude that it could give a significant contribution to the condensation nuclei (CCN) population. Although the flux from the leads were roughly an order of magnitude smaller and the leads cover only a small fraction of the pack ice, the local source may till be important for the CCN population in Arctic fogs. The primary marine aerosol source will increase both with increased wind speed and with decreased ice fraction and extent. The local CCN production may therefore increase and influence cloud or fog albedo and lifetime in response to greenhouse warming in the Arctic Ocean region.

Production Functions of Film Drops by Bursting Bubbles

Abstract Experimental results of Blanchard and Syzdek and of Resch and Afeti on the production of film drops by bubbles bursting at the surface of seawater were parameterized earlier by Wu. More recently, comprehensive observations have been carried out by Spiel. All these measurements, covering different size ranges of film drops, are shown to quantitatively complement each other. Through combining these results, the production of film drops has been quantified, in terms of both number and size distribution, over the entire radius range 0.01–250 μm. The average size of film drops is about 25 μm in radius, which is much larger than the commonly cited radius for film drops of 5 μm. In addition, all the results are shown to follow a simple rule; that is, the ratio between the total surface area of film drops and the surface area of their parent bubble is a constant.

Concentrations of Sea-Spray Droplets at Various Wind Velocities: Separating Productions through Bubble Bursting and Wind Tearing

Abstract There are two sets of comprehensive measurements of sea spray: de Leeuw and Smith et al. Their data are interpreted to describe similar productions of film and jet drops by bursting bubbles. For measurements of Smith et al., those droplets associated with the second peak at large sizes of the production spectrum are shown to be spume drops generated by the wind tearing of wave crests. Together with physical understanding, representations of field data are deduced for film and jet drops and are discussed for spume drops.

The Influence of Stratigraphy On Microwave Radiation From Natural Snow Cover

The present report discusses a structure dependent model of emissivity of snow cover. A snow cover was represented by a medium comprised of discrete scatterers. In the case of dry snow, ice grains stood for scatterers. For wet snow, two geometrical configurations of the water component were considered: I is a mixture of ice grains and water drops; II is a mixture of ice grains covered with water film and water drops. Scatters were assumed to have a spherical from and the lognormal distribution of sizes. Calculations of radiobrightness temperature of snow cover were made using data of glaciological measurements of its physical parameters and microstructure. Results of calculations were compared with measurements of radiobrightness temperature at various states of the snow cover.

On the births of film drops from bubbles bursting on seawater surfaces

The parameters describing the birth of film droplets originating from bubbles bursting on seawater surfaces are presented. Results are given for bubble sizes Db from 2 to 14.6 mm equivalent volume diameter. It is shown, contrary to earlier reports, that the films of all bubbles with Db up to at least 14.6 mm burst in an orderly manner in which a hole appears at a well‐defined location, usually the film's edge, and propagates from there gathering up the film's mass into a toroidal ring as it progresses. This process is enabled because surface tension provides the force required to sustain the centripetal accelerations. Film drops are created when beads, of sufficient size, form along the length of the toroidal ring and surface tension is insufficient to maintain the centripetal accelerations at these accumulation points. Pieces of the ring break loose and leave the toroidal ring along paths tangential to the bubble's cap. It is shown that only bubbles larger than 2.4 mm diameter can launch film droplets by this means and that this begins when the film has rolled up through an angle of about 31° independent of both bubble size and (theoretically) surface tension. Film drop spray patterns recorded on MgO‐coated cylindrical shells surrounding the burst bubbles yield film drop numbers and trajectories. In addition, film drop size distributions, their speed of launch, and the speed at which the film opens have been determined as a function of bubble size. The droplet sizes cited here are substantially larger than most previous estimates, and with a high probability, these droplets follow downward trajectories which lead them to impact the surface. A strong inference may be drawn that these impacts give birth to secondary droplets that are smaller than their parents and which have upward velocity components.

A hypothesis concerning the peak in film drop production as a function of bubble size

A hypothesis is advanced to explain the peak in film drop production as a function of bubble size observed by Blanchard and Syzdek [1988]. Evidence is presented that for bubble diameters less than about 3 mm, bubble films do not disintegrate but roll up, forming a toroidal ring that gains mass as it advances toward the film edge. It is suggested that film drops are created when this rolled‐up mass “hits” the edge of the film and hypothesized that the peak in production arises because of a competition between an increase in the mass of the rolled‐up toroid and a decrease in its speed as bubble size increases. In this scenario the location of the break in the film is an important parameter. Measurements of this break point are provided. The theory provides an estimate of the bubble size dependence of the number and size of the film drops. The predicted number of droplets per bubble is less and the droplet sizes are larger than the values reported by Blanchard and Syzdek. The theory uses one adjustable parameter that fits the onset of film drop production observed by Blanchard and Syzdek and, in so doing, glosses over the complexities of the toroid impact with the film edge. The possibility that some “film” drops are perhaps, in reality, jet drops generated by bubbles created by film drop impacts with the water's surface is advanced.

Film drops produced by air bubbles bursting at the surface of seawater

By taking together various observations on air bubbles bursting at the surface of seawater, the production rate and size spectrum of film drops are deduced. The number of film drops produced is proportional to the square of bubble diameter, and the size spectrum of film drops produced by bubbles of various diameters is universal. These are consistent with the concept that the numerical production of film drops is related physically to the surface area of the bubble film cap. The size spectrum of film drops can be described by a two‐segment power law: d−1/2 and d−2 divided at the droplet diameter d = 90 μm. Many film drops were observed having diameters much greater than the previously suggested diameters, 4–15 μm, separating the dominant contribution of film and jet drops.

Submicron film drop production by bubbles in seawater

The marine droplet aerosol, composed of the film and jet drops produced by breaking bubbles, is at the origin of most of the sea salt particles found in the atmosphere. For a long time, it was believed that the number of film drops produced per bubble burst increased continuously with increasing bubble diameter. Recently, however, Blanchard and Syzdek (1988) reported a peak in film drop production in the bubble size range of 2‐ to 2.5‐mm diameter, with much lower drop counts for larger bubbles. Experiments designed to investigate this peak over the bubble diameter range of 1.06–5.7 mm are reported. The results confirm the existence of a peak in the film drop count data at a bubble diameter of about 2.14 mm. The size distribution of the film drops accounting for the peak was estimated using a screen diffusion battery. Most of the drops were found to be of submicron dimensions and concentrated in the 0.05‐ to 0.3‐ μm‐diameter size range.

Bubble flux and marine aerosol spectra under various wind velocities

A complete size spectrum of bubbles in the near‐surface ocean is first deduced from available measurements. Combining this with the functional variation of bubble population with wind velocity, rates of bubbles arriving at the sea surface, expressed in the form of flux spectra, are obtained under various wind velocities. In the meantime, production of film and jet drops by artificially generated bubbles at the surface of seawater is parameterized. Spectra of marine aerosols under various wind velocities are finally obtained from the field‐determined bubble flux spectrum and the laboratory‐determined aerosol production function. The estimated spectra compare favorably with oceanic measurements.

Film drop distributions from bubbles bursting in seawater

The liquid droplets produced from the breaking up of the film cap of oceanic bubbles have long been considered as constituting a significant fraction of the marine aerosol. The size and number distributions of these film drops are investigated for single bubbles that burst in seawater under laboratory conditions. Optical particle detection and counting techniques are used to size the droplets generated from bubbles varying in diameter from about 1 to 6 mm. Parallel measurements are also made using a laser holographic setup for bubbles up to about 10 mm in diameter. Taken together, a film drop size spectrum extending from 0.8 to 500 μm is covered. From these results, an experimental correlation between the number of film drops generated and the parent bubble diameter is proposed. Based on this correlation and published data concerning the number of jet drops produced per bubble, a crossover point for bubbles that produce predominantly either film drops or jet drops is located at a bubble diameter of about 1.8 mm. In other words, bubbles larger than this threshold diameter produce more film drops than jet drops, while smaller bubbles generate more jet drops. A couple of film drops as large as 500 μm for a 10 mm bubble are detected. Although these maximum sizes diminish with decreasing bubble diameter, they happen to be much larger than previously thought.

Comment on “Film drop production as a function of bubble size” by D. C. Blanchard and L. D. Syzdek

Comment on “Film drop production as a function of bubble size” by D. C. Blanchard and L. D. Syzdek

Reply [to “Comment on ‘Film drop production as a function of bubble size’ by D. C. Blanchard and L. D. Syzdek”

Reply [to “Comment on ‘Film drop production as a function of bubble size’ by D. C. Blanchard and L. D. Syzdek”

N‐Alkanes, fatty acid esters, and fatty acid salts in size fractionated aerosols collected over the Mediterranean Sea

The n‐alkanes, fatty acid esters, and fatty acid salts have been analyzed in size fractionated aerosols collected over the Mediterranean Sea using a five‐stage cascade impactor. Two main sources of n‐alkanes have been identified: terrestrially derived n‐alkanes evenly distributed over the whole particle size spectrum and anthropogenic n‐alkanes predominantly carried by submicron particles. The comparison between the fatty acid ester (FAE) and fatty acid salt (FAS) particle size distributions allowed an important contribution to be ascertained of the marine source in aerosols ranging from 7.2 to 3.0 μm under rough weather conditions that may be due to larger bubble produced particles. In contrast, FAE and FAS were evenly distributed from the first to the fifth stage, when collected during calm sea surface conditions. Higher values of the degree of unsaturation of FAE and FAS were associated with mass concentration maxima observed on stages 2 and 3 in IMPI aerosol sample whereas lower values were found on the other stages in the same sample, and over the whole particle size spectrum in IMP2 aerosol sample collected during calm weather conditions. The data we present here are discussed in terms of jet and film drop ejections and degradation processes.

Distribution of the liquid aerosol produced from bursting bubbles in sea and distilled water

Laser holographic techniques are used to observe and measure the liquid droplets (film drops) produced by air bubbles bursting in both seawater and distilled water. Film drop aerosol production is found not only to be a function of parent bubble size but also of the type of water (sea or distilled) in which the bubbles burst. For bubbles in the diameter range of about 4 mm-10 mm, fewer but bigger film drops are observed for the distilled water sample. Furthermore, the mass of the droplets produced per bubble is found to be greater for bubbles that burst in distilled water. In general, the film drop size range shifts towards larger sizes as the diameter of the parent bubble is increased. The largest drop sizes measured are 680 μm in distilled water and 500 μm in seawater for a 10 mm bubble. These values happen to be much greater than those hitherto reported.

Comment on an article by J. Wu

In a recent publication, Wu (1989) has argued that the majority of the marine aerosol consists of jet drops as opposed to film drops. I would suggest that this conclusion is incorrect, being based on poor estimates of the oceanic flux of large bubbles. In addition, Wu relies entirely on a single study of film drop production which, whilst of great value, was restricted to the measurement of film drops of greater than 8 µm (Resch et al., 1986). Other studies have revealed that a far greater number of smaller film drops are produced (Blanchard and Syzdek, 1988). DOI: 10.1034/j.1600-0889.1990.t01-3-00008.x

Surface-active monolayers, bubbles, and jet drops

High-speed motion picture films (about 3000 frames per second) of bubbles of 0.7 and 1.3 mm diameter bursting at a seawater surface covered with an oleic acid monolayer show that the formation and behavior of the jet drops are profoundly influenced by the monolayer. It is doubtful, however, that monolayers on the surface of natural bodies of water exert as high a surface pressure as does an oleic acid monolayer. Natural monolayers probably affect film drop production more than that of the small jet drops that are important in atmospheric processes. DOI: 10.1034/j.1600-0889.1990.t01-1-00005.x