1,417 research outputs found
Why surface nanobubbles live for hours
We present a theoretical model for the experimentally found but
counter-intuitive exceptionally long lifetime of surface nanobubbles. We can
explain why, under normal experimental conditions, surface nanobubbles are
stable for many hours or even up to days rather than the expected microseconds.
The limited gas diffusion through the water in the far field, the cooperative
effect of nanobubble clusters, and the pinned contact line of the nanobubbles
lead to the slow dissolution rate.Comment: 5 pages, 3 figure
Inert gas accumulation in sonoluminescing bubbles
In this paper we elaborate on the idea [Lohse et al., Phys. Rev. Lett. 78,
1359-1362 (1997)] that (single) sonoluminescing air bubbles rectify argon. The
reason for the rectification is that nitrogen and oxygen dissociate and their
reaction products dissolve in water. We give further experimental and
theoretical evidence and extend the theory to other gas mixtures. We show that
in the absence of chemical reactions (e.g., for inert gas mixtures) gas
accumulation in strongly acoustically driven bubbles can also occur.Comment: J. Chem. Phys., in press (to appear in November 1997), 30 pages, 15
eps-figure
23. Areogeophysical Investigations over the Bowers Mountains, North Victoria Land; Antarctica
Order-to-disorder transition in ring-shaped colloidal stains
A colloidal dispersion droplet evaporating from a surface, such as a drying
coffee drop, leaves a distinct ring-shaped stain. Although this mechanism is
frequently used for particle self-assembly, the conditions for crystallization
have remained unclear. Our experiments with monodisperse colloidal particles
reveal a structural transition in the stain, from ordered crystals to
disordered packings. We show that this sharp transition originates from a
temporal singularity of the flow velocity inside the evaporating droplet at the
end of its life. When the deposition speed is low, particles have time to
arrange by Brownian motion, while at the end, high-speed particles are jammed
into a disordered phase.Comment: accepted for PR
Quantifying microbubble clustering in turbulent flow from single-point measurements
Single-point hot-wire measurements in the bulk of a turbulent channel have
been performed in order to detect and quantify the phenomenon of preferential
bubble accumulation. We show that statistical analysis of the bubble-probe
colliding-times series can give a robust method for investigation of clustering
in the bulk regions of a turbulent flow where, due to the opacity of the flow,
no imaging technique can be employed. We demonstrate that micro-bubbles (radius
R_0 ~ 0.1 mm) in a developed turbulent flow, where the Kolmogorov length-scale
is, eta ~ R_0, display preferential concentration in small scale structures
with a typical statistical signature ranging from the dissipative range,
O(eta), up to the low inertial range, O(100 eta). A comparison with
Eulerian-Lagrangian numeri- cal simulations is also presented to further
support our proposed way to characterize clustering from temporal time series
at a fixed position.Comment: 7 pages, 4 figure
Nonmonotonic settling of a sphere in a cornstarch suspension\ud
Cornstarch suspensions exhibit remarkable behavior. Here, we present two unexpected observations for a sphere settling in such a suspension: In the bulk of the liquid the velocity of the sphere oscillates around a terminal value, without damping. Near the bottom the sphere comes to a full stop, but then accelerates again toward a second stop. This stop-go cycle is repeated several times before the object reaches the bottom. We show that common shear thickening or linear viscoelastic models cannot account for the observed phenomena, and propose a minimal jamming model to describe the behavior at the botto
Universal mechanism for air entrainment during liquid impact
When a mm-sized liquid drop approaches a deep liquid pool, both the interface
of the drop and the pool deform before the drop touches the pool. The build up
of air pressure prior to coalescence is responsible for this deformation. Due
to this deformation, air can be entrained at the bottom of the drop during the
impact. We quantify the amount of entrained air numerically, using the Boundary
Integral Method (BIM) for potential flow for the drop and the pool, coupled to
viscous lubrication theory for the air film that has to be squeezed out during
impact. We compare our results to various experimental data and find excellent
agreement for the amount of air that is entrapped during impact onto a pool.
Next, the impact of a rigid sphere onto a pool is numerically investigated and
the air that is entrapped in this case also matches with available experimental
data. In both cases of drop and sphere impact onto a pool the numerical air
bubble volume V_b is found to be in agreement with the theoretical scaling
V_b/V_{drop/sphere} ~ St^{-4/3}, where St is the Stokes number. This is the
same scaling that has been found for drop impact onto a solid surface in
previous research. This implies a universal mechanism for air entrainment for
these different impact scenarios, which has been suggested in recent
experimental work, but is now further elucidated with numerical results
- …