Donald E. Spiel

A Model of Marine Aerosol Generation Via Whitecaps and Wave Disruption

We have, over the past several years, as one element in the development of a time-dependent model of the aerosol population of the marine atmospheric boundary layer, attempted to define, in terms of aerosol droplet radius (r) and 10m-elevation wind speed (U), a model of open-ocean sea-surface aerosol generation. This source function is represented by the expression dF(r, U)/dr, which states the rate of production of marine aerosol droplets, per unit area of the sea surface, per increment of droplet radius. In the initial modeling efforts only the indirect aerosol production mechanisms associated with the bursting of whitecap bubbles (see Figure 1) were considered. The model for sea surface aerosol generation by the indirect mechanisms, first introduced in our Canberra SSAG-1 (Monahan, et al, 1979) and Manchester SSAG-2 (Monahan, 1980) papers, is given by Equation 1, where W is the

The number and size of jet drops produced by air bubbles bursting on a fresh water surface

{\rm{d}}{{\rm{F}}_0}/{\rm{dr = W}}{\tau ^{ - 1}}{\rm{dE/dr}}

More on the births of jet drops from bubbles bursting on seawater surfaces

instantaneous fraction of the sea surface covered by whitecaps, τ is the time constant characterizing the exponential whitecap decay (measured in seconds), and dE/dr is the differential whitecap aerosol productivity, i.e. the number of droplets per increment droplet radius produced during the decay of a unit area of whitecap (expressed in m−2 μm−1 ). The necessary expression for W(U) was obtained from shipboard photographic observations of white- caps (Monahan, 1971; Toba and Chaen, 1973), while values for τ and dE/dr were derived from measurements made using the University College, Galway, whitecap simulation tank.

Acoustical measurements of air bubbles bursting at a water surface: Bursting bubbles as Helmholtz resonators

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 films edge, and propagates from there gathering up the films 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 bubbles 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

The size distributions of the jet drops produced by individual air bubbles bursting on a fresh water surface are presented. The bubbles studied ranged in size from 349 to 1479 μm radius. The probability that a bubble of radius rb produces at least n drops, p(rb, n), is given for n up to 7. The underwater sound made by collapsing bubbles is discussed briefly.

Turbulent Transport and Evaporation of Droplets Generated at an Air-Water Interface

Superconducting films of tin and indium on supporting substrates have functioned successfully as detectors of individual nuclear particles. The films are sufficiently thin and narrow that individual α‐particle impacts initiate superconducting to normal transitions which spread, in the presence of a transport current, to span a full film cross section. The transitions are observed by means of the ir drop produced by a transport current. For low current densities self‐terminating voltage pulses of a few nsec duration are observed. At higher current densities the boundaries of a normal region initiated by an α particle propagate by Joule heating to the ends of the film. The range of the 5.3‐MeV α particles utilized for these experiments greatly exceeds the 0.1 μm thickness of the films and the resulting deposition of energy in the substrate affects the response of any film which is in direct contact with its substrate. The introduction of a thin thermally insulating layer of varnish between the film and its ...

Characteristics of over-water surface stress during strex

The parameters of the births of jet drops originating from bubbles bursting on seawater surfaces are presented. This report supplements an earlier one by providing the birth times and heights of all the jet drops, not just the top. Results are given for bubble sizes from 350- to 1500-μm equivalent volume radius. The ejection speeds of the jet droplets generated by a collapsing bubble and the height above the surface, as well as the time, at which all the drops break off the ascending jet have been measured. For the bubble sizes used in this study, the first drop emitted, the top drop, is closest to the surface at birth, the second is the highest, and all subsequent drops are at intermediate heights. Furthermore, each drop after the second is born at a height that is lower than the drop that preceded it. Size distributions of the jet drops from each of 10 bubble sizes are reported. They differ from size distributions published earlier in that the sizes of the lower drops are not bimodally distributed. This difference is attributed to a difference in water temperature.

The Droplets Produced by Individual Bubbles Bursting on a Sea Water Surface

Evidence is presented that air bubbles bursting at the surface of water are Helmholtz resonators. The detection by an acoustic transducer of the aerosols generated by the collapsing bubble is also demonstrated. The use of this detector to measure such parameters as bubble collapse time, the number and spacing of the jet drops, their ejection velocities, and their size is discussed.