Session E08: Bubbles: Rupture

Aerosolization of crude oil-dispersant slicks due to popping of bubbles

Aerosolization of crude oil after spills due to the popping of bubbles on the ocean surface is one of the mechanisms by which the oil ejects into the atmosphere. Little is known about the effect of the oil physicochemical properties on the size distributions of these aerosols. In this study, bubble plumes with mode diameters of 86 µm (small), 178 µm (medium) and 595 µm (large) are injected into a seawater column covered by slicks of crude oil, Corexit 9500A dispersant, and premixed dispersant and crude oil at a ratio (DOR) of 1:25. Focusing on the sub-micron scales, in the presence of ambient air, the large bubbles cause an order of magnitude increase in the concentration of nano-aerosols for 500 µm thick slick of  DOR-1:25, and 50 µm slick of pure dispersant. The elevated concentration decays slowly (>20 min) after the bubble injection stops. To elucidate the latter phenomenon, additional tests show that although the increase in nano-droplet concentration persists, the decay is immediate in the presence of pure air. In ambient air, the increase is higher, and the decay is slower. Coating the tank walls with oil-absorbing pads accelerated the decay after bubble plume stops, suggesting the secondary production originating from the tank walls contributes to the slow decay

  

Bubble bursting: Universal cavity and jet profiles

After a bubble bursts at a liquid surface, the collapse of the cavity generates capillary waves, which focus on the axis of symmetry to produce a jet. The cavity and jet dynamics are primarily controlled by a non-dimensional number that compares capillary inertia and viscous forces, i.e. the Laplace number La=ργR₀/μ², where ρ, μ, γ and R₀ are the liquid density, viscosity, interfacial tension, and the initial bubble radius, respectively. In this paper, we show that the time-dependent profiles of cavity collapse (t<t₀) and jet formation (t>t₀) both obey a |t - t0|^2/3 inviscid scaling, which results from a balance between surface tension and inertia forces. Moreover, we present a universal scaling, valid above a critical Laplace number, which reconciles the time-dependent scaling with the recent scaling theory that links the Laplace number to the final jet velocity and ejected droplet size. This leads to a single universal self-similar formula which describes the full history of the jetting process, from cavity collapse to droplet formation.   

Bubble pinch off in a turbulent flow

We present experiments and direct numerical simulations of the break-up of bubbles in a turbulent flow.  The turbulent flow induces bubble deformation, creating a neck that then pinches off giving birth to child bubbles. We focus on the transition from the deformation regime controlled by the turbulent fluctuations to the final universal pinch-off, which present a self-similar dynamics, similar to the one reported in bubble pinch-off in still water. We characterize the large scale deformation of the bubble by its aspect ratio and observe fluctuations at the order of the eddy turnover scale, while the final pinch-off starts above a critical deformation, typically one millisecond prior to break-up. Over this last millisecond, the necking follows a universal self-similar behavior, independent of the turbulent flow.