796 research outputs found
Walks of bubbles on a hot wire in a liquid bath
When a horizontal resistive wire is heated up to the boiling point in a
subcooled liquid bath, some vapor bubbles nucleate on its surface. Traditional
nucleate boiling theory predicts that bubbles generated from active nucleate
sites, grow up and depart from the heating surface due to buoyancy and inertia.
However, we observed here a different behavior: the bubbles slide along the
heated wire. In this situation, unexpected regimes are observed; from the
simple sliding motion to bubble clustering. We noticed that bubbles could
rapidly change their moving direction and may also interact. Finally, we
propose an interpretation for both the attraction between the bubbles and the
wire and for the motion of the bubbles on the wire in term of Marangoni
effects
Granular size segregation in underwater sand ripples
We report an experimental study of a binary sand bed under an oscillating
water flow. The formation and evolution of ripples is observed. The appearance
of a granular segregation is shown to strongly depend on the sand bed
preparation. The initial wavelength of the mixture is measured. In the final
steady state, a segregation in volume is observed instead of a segregation at
the surface as reported before. The correlation between this phenomenon and the
fluid flow is emphasised. Finally, different ``exotic'' patterns and their
geophysical implications are presented.Comment: 8 page
Resonant and antiresonant bouncing droplets
When placed onto a vibrating liquid bath, a droplet may adopt a permanent
bouncing behavior, depending on both the forcing frequency and the forcing
amplitude. The relationship between the droplet deformations and the bouncing
mechanism is studied experimentally and theoretically through an asymmetric and
dissipative bouncing spring model. Antiresonance effects are evidenced.
Experiments and theoretical predictions show that both resonance at specific
frequencies and antiresonance at Rayleigh frequencies play crucial roles in the
bouncing mechanism. In particular, we show that they can be exploited for
droplet size selection.Comment: 4 pages, 4 figures and 1 vide
A fountain of droplets
A vessel is plunged upside down into a pool of 50 cSt silicone oil. An air
bell is then created. This bell is vertically shaken at 60 Hz that leads to the
oscillation of the air/oil interface. The edges of the immersed vessel generate
surface waves that propagate towards the center of the bell. When the amplitude
of the oscillation increases, wave amplitude increases. We study the influence
of the angle between successive sides on the wave patterns. Two kinds of vessel
have been studied: a triangular and a square prism. The shape of the air/oil
meniscus depends on the angle between the sides of the considered prism. As the
amplitude of the oscillation is increased, the triple line, which is the
contact line between the solid and the air/oil interface, moves up and down.
Above a given acceleration that depends on the immersion depth and on the shape
vessel, wave goes under the corner edge of the bell. During the oscillation,
the wave generates at the edges presents a singularity that leads eventually to
a jet and a drop ejection. A drop is ejected at each oscillation. More
complicated ejection can be produced with further increase of the amplitude.
This is a sample arXiv article illustrating the use of fluid dynamics videos.Comment: 3 pages, 2 figures, 2 movies (high-res and low-res
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