Experimental study of PERIODIC OSCILLATION of RISING BUBBLES

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Experimental studyof PERIODIC OSCILLATION of
RISING BUBBLES

• Kamil Wichterle,
• Katerina Machacová,
• Pavel Raška,
• and
• Marek Vecer

VŠB-Technical University of Ostrava, Department
of Chemistry, 70833 Ostrava Poruba, CR
Institut of Chemical Process Fundamentals
ASCR, 16502 Prague 6 Suchdol, CR
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RISING BUBBLES

• MACROSCALE
• Bubble plume (treatment of liquid steel by
  oxygen and argon)

QUESTIONS ?

• MICROSCALE
• Single bubble
• ANSWERS

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RISING BUBBLES

• Theory
• Simple models for small spherical bubbles
• CFD models of symmetrical bubbles
• Sophisticated CFD complete models
• Experiments
• Short-time qualitative observations
• Short-time quantitative records
• Quantitative data suitable for statistics

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LEVITATING BUBBLES
Divergent downstream flow
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Overall view
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(No Transcript)
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LEVITATING BUBBLE VB 300 mm3, dB 8.3 mm
5 x slower
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PERIODICITY angle aX 10 seconds record
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AUTOCORRELATION
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AUTOCORRELATION
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FREQUENCY
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REAL RISING BUBBLES
increasing volume
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BUBBLE SHAPE
Surface tension
Hydrostatics
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SYMMETRIC OBLATE BUBBLE
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LOWER DRAG (hypothetical)
Why not ??
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INCLINED BUBBLE in low-viscosity liquid
Buoyancy higher
Buoyancy lower
Hydrostatic pressure lower
Radius lower
Hydrostatic pressure higher
Surface forces
Radius higher
Drag
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Equation of oscillatory harmonic motion
for ellipsoidal bubbles in water f  6-9 Hz
StL 0.08
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STROUHAL NUMBER
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DRIFT
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BUBBLE WOBBLING AND DRIFT
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BUBBLE PATH UPPER PROJECTION Is it hellical or
zig-zag ?
Horizontal component of velocity Horizontal
component of acceleration
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SHAPE OF PATH UPPER PROJECTION
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• Conclusion
• Experimental
• Bubble position in downstream divergent liquid
  flow were recorded by high speed camera.
  Ellipsoidal bubbles of volumes 50  400 mm3 in
  water or glycerol solutions were studied.
• By autocorrelation analysis of horizontal
  trajectories of bubbles and of their wobbling
  observed in two projections, characteristic
  frequencies were determined.
• Statistical analysis of the horizontal bubble
  velocity and its acceleration revealed the most
  probable ellipsoidal pattern of drift motion.
• For the medium size bubbles under investigation,
  the drift pattern is essentially zig-zag, while
  the helical pattern is more probable for smaller
  ones.

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• 2. Theoretical
• Force balance for ellipsoidal bubbles rising
  in low viscosity liquids (1ltEolt40, Re gt100)
  explains
• Oscillatory wobbling of the bubble is caused by
  non-linear compensation of external forces by
  surface tension.
• Characteristic frequency of wobbling can be
  predicted. The frequency depends on the rising
  velocity and material properties effect of the
  bubble size is minor.
• The horizontal drift is related to the bubble
  wobbling and its frequency is identical.
• Its velocity is comparable with the rising
  velocity.
• Amplitude of the horizontal drift decreases with
  increasing viscosity and increases with bubble
  size.

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Current research TWO LEVITATING BUBBLES
DRIFT
Liquid flow
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TWO LEVITATING BUBBLES VB 300 mm3, dB 8.3 mm

5 x slower
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Katerina Machacová Pavel Raška Lenka
Kulhánková Jana Wichterlová Marek VecerMarek
C. RužickaJirí Drahoš
Generous support of the Grant Agency of the
Czech Republic through the projects 104/04/0827
and 104/06/P287 is acknowledged.
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Thank you for the attention
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Technical University of Ostrava
Ostrava surrounding
Thank you for the attention
Ostrava industry
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LEVITATING BUBBLE VB 50 mm3, dB 4.6 mm
5 x slower