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Experimental study of PERIODIC OSCILLATION of RISING BUBBLES

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Hydrostatics. Surface tension. BUBBLE SHAPE. SYMMETRIC OBLATE BUBBLE. Drag. Buoyancy ... Hydrostatic. pressure. higher. Surface forces. Resulting force ... – PowerPoint PPT presentation

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Title: Experimental study of PERIODIC OSCILLATION of RISING BUBBLES


1
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
2
RISING BUBBLES
  • MACROSCALE
  • Bubble plume (treatment of liquid steel by
    oxygen and argon)

QUESTIONS ?
  • MICROSCALE
  • Single bubble
  • ANSWERS

3
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

4
LEVITATING BUBBLES
Divergent downstream flow
5
Overall view
6
(No Transcript)
7
LEVITATING BUBBLE VB 300 mm3, dB 8.3 mm
5 x slower
8
PERIODICITY angle aX 10 seconds record
9
AUTOCORRELATION
10
AUTOCORRELATION
11
FREQUENCY
12
REAL RISING BUBBLES
increasing volume
13
BUBBLE SHAPE
Surface tension
Hydrostatics
14
SYMMETRIC OBLATE BUBBLE
15
LOWER DRAG (hypothetical)
Why not ??
16
INCLINED BUBBLE in low-viscosity liquid
Buoyancy higher
Buoyancy lower
Hydrostatic pressure lower
Radius lower
Hydrostatic pressure higher
Surface forces
Radius higher
Drag
17
Equation of oscillatory harmonic motion
for ellipsoidal bubbles in water f  6-9 Hz
StL 0.08
18
STROUHAL NUMBER
19
DRIFT
20
BUBBLE WOBBLING AND DRIFT
21
BUBBLE PATH UPPER PROJECTION Is it hellical or
zig-zag ?
Horizontal component of velocity Horizontal
component of acceleration
22
SHAPE OF PATH UPPER PROJECTION
23
  • 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.

24
  • 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.

25
Current research TWO LEVITATING BUBBLES
DRIFT
Liquid flow
26
TWO LEVITATING BUBBLES VB 300 mm3, dB 8.3 mm

5 x slower
27
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.
28
Thank you for the attention
29
Technical University of Ostrava
Ostrava surrounding
Thank you for the attention
Ostrava industry
30
LEVITATING BUBBLE VB 50 mm3, dB 4.6 mm
5 x slower
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